Renamed 'repo_hooks' function to '_ProjectHooks'.

This renaming was done for two reasons:
1. The hooks are actually project-level hooks, not repo-level
   hooks.  Since we are talking about adding repo-level hooks,
   It keeps things less confusing if we name the existing hooks
   to be "ProjectHooks"
2. The function is a private function in and so
   should have capitalization to match.

I also added a docstring describing this function.

Change-Id: I1d30f5de08e8f9f99f78146e68c76f906782d97e
1 file changed