Add Uru Ruby version manager

Uru is a lightweight, multi-platform command line tool that helps you
use the multiple rubies (currently MRI, JRuby, and Rubinius) on your
32/64-bit Linux, OS X, or Windows systems.

https://bitbucket.org/jonforums/uru
Build Uru from source
Remove redundant version tag
Add newline before dependencies
Use double quoted strings instead of single
Build Uru from downloaded tarball, not go get
Use install to setup go workspace
Remove hashmarks from caveats
Remove superfluous info from caveats
uru: add 0.7.4 bottle.