Factor MixtureDriver out of PitmanYor::Mixture (broken)
Merge branch 'master' into mixture-driver

Conflicts:
	include/distributions/clustering.hpp
Get most of tests passing; example/mixture segfaults
Fix bug in PitmanYor::Mixture
Merge pull request #37 from forcedotcom/mixture-driver

Mixture driver
Refactor models toward a Shared state struct.
Add typedefs to mixture.
Remove typedefs from Model.
Remove backwards-compatibility typedefs.
Remove name functions from Model.
Move basic scorers and samplers to namespace.
Start refactoring python for Shared.
Prepare for python Shared rename.
Name Shared values appropriately in tests.
Refactor io mixins and cython wrappings.
Split cython boilerplate from customization.
Refactor python models to new layout.
Fix model formatting.
Rename Model to Shared in c++.