Move Linux compatibility scripts from osx/ to unix/.
setup: Source the user's profile early.

This allows commands provided by this repository to be used later in the setup.
Specifically the sensible-browser/xdg-open command on non-Linux operating
systems such as Mac OS X.
Improve the language in the readme a wee bit.
Add git completion to my ~/.bashrc on Debian.

The install-git-completion script does this automatically.
Add ~/.rvm/bin to my path on Debian.

The install-rvm script does this automatically.