Get redshift into pip

[syllog1sm]

Requires figuring out what to do about the dependency on sparsehash.

[antoniomo]

A lot of python/cython packages just assume that the non-python dependencies are already there and try to build, just failing if the dependency isn't installed. That and some installation instructions in the readme (do apt-get install sparsehash on ubuntu/debian, brew install google-sparsehash on osx, who knows what on windows, prior to pip install redshift) is enough in most cases.