Experimental implementation of canonicalization.
Added barebones unstructured freq model, with __init__ addressing #14.
New (highly!) experimental features using macros.
Merge pull request #19 from ysanders/master

ProductDistribution can now handle any non-zero number of factors
Fixed docstrings in macro-generated models.
Caught up to master.
Merge pull request #18 from csferrie/feature-experimental

New (highly!) experimental features using macros.
Changed how unstructured_models exports.
changed default to canonicalize=True
Added canonicalization support to BinomialModel.

This involves refactoring the way derived models work to use a
shared base class that passes through methods like
canonicalize.
Continued work on refactoring into DerivedModel.
Merge branch 'master' into feature-canonicalize
Added derived_models to __init__.
Possibly breaking change to address #22. Refactoring into DerivedModel.
Fixed stupid syntax error in previous commit.
Missed method on DerivedModel in refactoring.
Fix for picking of DVPM, deprecation of _serial_model, fix for m_c.
Fix noted by IH.
...and a typo.
Merge pull request #20 from csferrie/feature-canonicalize

Model parameter canonicalization