Document recent breaking changes in router.
Start updating router docs.
More updates to routing docs.
Move REST routing into the routing chapter.
Remove section that doesn't need to be explicit.

I think the newest changes to Router make it fast enough that we don't
have to give more instruction to people.
Expand reverse routing docs a bit.
Shift more content around.

Stop using the API sections of the docs, and inline method annotations
as we started to do in the ORM docs.
Move more API docs into relevant section.
Add notable point to migration guide.
Merge pull request #1455 from cakephp/3.0-routing

3.0 routing