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
uru: add 0.7.4 bottle.