docs(guide/overview): Refactor overview and mvc docs

Before, there we multiple overview docs:
- guide/overview
- guide/introduction
- guide/dev_guide.mvc
- guide/dev_guide.mvc.understanding_model
- guide/dev_guide.mvc.understanding_view
- guide/concepts

Now we have:
- guide/introduction: High level description of Angular with the key benefits but without code or any concrete concepts
- guide/concepts: explains all important concepts with a simple example and contains deep links to the other parts of the guide.

 All the old information was moved into existing documents or deleted when they were duplicates.

1 files changed, 102 insertions, 30 deletions

diff --git a/docs/content/guide/introduction.ngdoc b/docs/content/guide/introduction.ngdoc
index dfd9e21a..415801a7 100644
--- a/docs/content/guide/introduction.ngdoc
+++ b/docs/content/guide/introduction.ngdoc
@@ -1,42 +1,114 @@
 @ngdoc overview
-@name Developer Guide: Introduction
+@name Introduction
 @description
 
-Angular is pure client-side technology, written entirely in JavaScript. It works with the
-long-established technologies of the web (HTML, CSS, and JavaScript) to make the development of
-web apps easier and faster than ever before.
 
-One important way that Angular simplifies web development is by increasing the level of abstraction
-between the developer and most low-level web app development tasks. Angular automatically takes
-care of many of these tasks, including:
+# What Is Angular?
 
-  * DOM Manipulation
-  * Setting Up Listeners and Notifiers
-  * Input Validation
+AngularJS is a structural framework for dynamic web apps. It lets you use HTML as your template
+language and lets you extend HTML's syntax to express your application's components clearly and
+succinctly. Out of the box, it eliminates much of the code you currently write through data
+binding and dependency injection. And it all happens in JavaScript within the browser, making it
+an ideal partner with any server technology.
 
-Because Angular handles much of the work involved in these tasks, developers can concentrate more
-on application logic and less on repetitive, error-prone, lower-level coding.
+Angular is what HTML would have been had it been designed for applications. HTML is a great
+declarative language for static documents. It does not contain much in the way of creating
+applications, and as a result building web applications is an exercise in *what do I have to do
+to trick the browser into doing what I want.*
 
-At the same time that Angular simplifies the development of web apps, it brings relatively
-sophisticated techniques to the client-side, including:
+The impedance mismatch between dynamic applications and static documents is often solved with:
 
-  * Separation of data, application logic, and presentation components
-  * Data Binding between data and presentation components
-  * Services (common web app operations, implemented as substitutable objects)
-  * Dependency Injection (used primarily for wiring together services)
-  * An extensible HTML compiler (written entirely in JavaScript)
-  * Ease of Testing
+  * **a library** - a collection of functions which are useful when writing web apps. Your code is
+    in charge and it calls into the library when it sees fit. E.g., `jQuery`.
+  * **frameworks** - a particular implementation of a web application, where your code fills in
+    the details. The framework is in charge and it calls into your code when it needs something
+    app specific. E.g., `knockout`, `ember`, etc.
 
-These techniques have been for the most part absent from the client-side for far too long.
 
-## Single-page / Round-trip Applications
+Angular takes another approach. It attempts to minimize the impedance mismatch between document
+centric HTML and what an application needs by creating new HTML constructs. Angular teaches the
+browser new syntax through a construct we call directives. Examples include:
 
-You can use Angular to develop both single-page and round-trip apps, but Angular is designed
-primarily for developing single-page apps. Angular supports browser history, forward and back
-buttons, and bookmarking in single-page apps.
+  * Data binding, as in `{{}}`.
+  * DOM control structures for repeating/hiding DOM fragments.
+  * Support for forms and form validation.
+  * Attaching code-behind to DOM elements.
+  * Grouping of HTML into reusable components.
 
-You normally wouldn't want to load Angular with every page change, as would be the case with using
-Angular in a round-trip app. However, it would make sense to do so if you were adding a subset of
-Angular's features (for example, templates to leverage angular's data-binding feature) to an
-existing round-trip app. You might follow this course of action if you were migrating an older app
-to a single-page Angular app.
+
+
+## A complete client-side solution
+
+Angular is not a single piece in the overall puzzle of building the client-side of a web
+application. It handles all of the DOM and AJAX glue code you once wrote by hand and puts it in a
+well-defined structure. This makes Angular opinionated about how a CRUD application should be
+built. But while it is opinionated, it also tries to make sure that its opinion is just a
+starting point you can easily change. Angular comes with the following out-of-the-box:
+
+  * Everything you need to build a CRUD app in a cohesive set: data-binding, basic templating
+    directives, form validation, routing, deep-linking, reusable components, dependency injection.
+  * Testability story: unit-testing, end-to-end testing, mocks, test harnesses.
+  * Seed application with directory layout and test scripts as a starting point.
+
+
+## Angular Sweet Spot
+
+Angular simplifies application development by presenting a higher level of abstraction to the
+developer. Like any abstraction, it comes at a cost of flexibility. In other words not every app
+is a good fit for Angular. Angular was built with the CRUD application in mind. Luckily CRUD
+applications represent the majority of web applications. To understand what Angular is
+good at, though, it helps to understand when an app is not a good fit for Angular.
+
+Games and GUI editors are examples of applications with intensive and tricky DOM manipulation.
+These kinds of apps are different from CRUD apps, and as a result are probably not a good fit for Angular.
+In these cases it may be better to use a library with a lower level of abstraction, such as `jQuery`.
+
+# The Zen of Angular
+
+Angular is built around the belief that declarative code is better than imperative when it comes
+to building UIs and wiring software components together, while imperative code is excellent for
+expressing business logic.
+
+
+  * It is a very good idea to decouple DOM manipulation from app logic. This dramatically improves
+    the testability of the code.
+  * It is a really, _really_ good idea to regard app testing as equal in importance to app
+    writing. Testing difficulty is dramatically affected by the way the code is structured.
+  * It is an excellent idea to decouple the client side of an app from the server side. This
+    allows development work to progress in parallel, and allows for reuse of both sides.
+  * It is very helpful indeed if the framework guides developers through the entire journey of
+    building an app: from designing the UI, through writing the business logic, to testing.
+  * It is always good to make common tasks trivial and difficult tasks possible.
+
+
+
+Angular frees you from the following pains:
+
+  * **Registering callbacks:** Registering callbacks clutters your code, making it hard to see the
+    forest for the trees. Removing common boilerplate code such as callbacks is a good thing. It
+    vastly reduces the amount of JavaScript coding _you_ have to do, and it makes it easier to see
+    what your application does.
+  * **Manipulating HTML DOM programmatically:** Manipulating HTML DOM is a cornerstone of AJAX
+    applications, but it's cumbersome and error-prone. By declaratively describing how the UI
+    should change as your application state changes, you are freed from low-level DOM manipulation
+    tasks. Most applications written with Angular never have to programmatically manipulate the
+    DOM, although you can if you want to.
+  * **Marshaling data to and from the UI:** CRUD operations make up the majority of AJAX
+    applications' tasks. The flow of marshaling data from the server to an internal object to an HTML
+    form, allowing users to modify the form, validating the form, displaying validation errors,
+    returning to an internal model, and then back to the server, creates a lot of boilerplate
+    code. Angular eliminates almost all of this boilerplate, leaving code that describes the
+    overall flow of the application rather than all of the implementation details.
+  * **Writing tons of initialization code just to get started:** Typically you need to write a lot
+    of plumbing just to get a basic "Hello World" AJAX app working. With Angular you can bootstrap
+    your app easily using services, which are auto-injected into your application in a {@link
+    http://code.google.com/p/google-guice/ Guice}-like dependency-injection style. This allows you
+    to get started developing features quickly. As a bonus, you get full control over the
+    initialization process in automated tests.
+
+
+# Watch a Presentation About Angular
+
+Here is a presentation on Angular from May 2012. The {@link http://mhevery.github.io/angular-demo-slides/index.html#/list corresponding slides} are also available.
+
+<iframe width="560" height="315" src="http://www.youtube.com/embed/bfrn5VNpwsg" frameborder="0" allowfullscreen></iframe>