Major upgrade to Homebrew.jl functionality

All bright and ready for the 0.3 release, here's a nice overhaul of Homebrew.jl.  Features:

* Now runs off of mainline Homebrew instead of my own fork.  A little noisier in places, but much better overall as this means bottled formulae from mainline Homebrew will automatically be included.

* Hand-in-hand with the above, should transparently allow installation of properly bottled formulae from mainline Homebrew now, with no work done by `Homebrew.jl` maintainers

* Now has a much nicer/more complete programming interface