Add controllers

Public pages are pretty much done.

To check it out:

Open rails console and make a couple repos.

In the browser,

go to `/:username`, your repos should be listed
go to `/:username/:repo_name/new` to make a new post
go to `/:username/:repo_name` to list the posts
go to `/:username/:repo_name/:post_slug/edit` to update the post

Still have to do:
Apply authorization.
Add buttons for authenticated users to do things.
Add a way to add new repositories.