Updated INSTALL.rst to include new branch and Anaconda

Merge pull request pymc-devs#557 from pymc-devs/2.3_slice

Slice sampler and 2.3.3 prep

Incremented PyMC version to 2.3.2

Incremented version numbers

Fixed failure in ScipyDistributions

Removed alpha designation

alpha release for 3.0

Version 2.2

Changed version to 2.2beta

Typographical fixes