Enable tmux to send-prefix using C-a a

* It's useful when you have a tmux session into another tmux session
  (ie. via ssh).
Add puppet module
Fix gitconfig colors causing iTerm with solarized to show diffs incorrectly
Changed reference to prezto master
Go back to using skwp prompt for rvm-prompt integration
Merge pull request #402 from imobach/master

Enable tmux to send-prefix using C-a a