Add 'remote' argument to heroku

Also add the shorter -a switch to the app argument
Add remote argument completions

This was copied from _git-flow
Namespace git commands under heroku
Merge pull request #128 from pcasaretto/add-remote-argument-to-heroku

Add 'remote' argument to heroku
Merge pull request #133 from zhaocai/brew

_brew update
Merge pull request #134 from zhaocai/feature/_gem

_gem: update for browse, edit and clone commands