Implementation of multiple router pipelines

Here is what is pending:

1. Change controllers to go to back to `plug` instead of `before_action`
2. Discuss an alternate syntax for pipelines
3. Rebase!

Thoughts so far is welcome!

https://gist.github.com/chrismccord/3a3d1fd6f2f5d2bfd6d7 
We should not, that's what the todo is about. :) I think I will just move this function `Phoenix.Controller`.