Bundle Github color scheme

Fixes https://github.com/thoughtbot/dotfiles/issues/79
Replace s shell script with rspec shell function and alias

* Use a regular alias to make `s` short for `rspec`
* Use an `rspec` shell function to route to zeus when appropriate
* Removes confusion from `s` working differently than `rspec`
* Removes need to use a special alias to get zeus working
Merge branch 'dc-github-color' into upstream
Add aliases for most common git commands
Merge with thoughtbot upstream.
Merge branch 'upstream/master'

Merging in Thoughtbot updates.