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.

The current logo looks awful on high-density displays.  SVG is a
better choice because it can scale to any resolution without
increasing file size.

Amending #2775 to add support for IE 8 by falling back to existing PNG
with img.onerror

Using relative URLs as directed by @btford and @petebacondarwin.

(commit by Brenton Simpson - @appsforartists)

Closes #2874

also contains all kinds of fixes that I had to make in the docs app to
get the tutorial to render correctly

And update the link in the tutorial as well...