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.

When navigating to URLs such as
docs.angularjs.org/api/ng#filter, the browser
was not able to navigate to the named anchor,
"filter," because the anchor did not yet exist
in the DOM.

This fix uses the $anchorScroll service
to automatically scroll to the right place when
the content has been added to the page.

Fixes #4703

Fixes some warnings during docs generation.

Closes #4673

Closes 4611

Closes #4619