New Modeling Kernel
-------------------

This commit adds a new modeling kernel based on
[Boost.polygon](http://www.boost.org/doc/libs/1_58_0/libs/polygon/doc/index.htm).
It currently supports a very limited set of operations:

+ Creation a model.
+ Creation of model vertices.
+ Creation of model edges.

Internally, an edge split operation is provided but not yet exposed.

Miscellany
----------

+ Fix a bug in attribute association.
  Because model entity items in attributes may have a membership mask,
  calling `setValue()` does not guarantee that the association will
  occur. Return the proper boolean or infinite recursion will occur
  inside `Attribute::associateEntity()`.
+ Add a Python-callable variant of ImportJSON::ofLog.
+ Have `smtk.simple` hang on to operator results so that scripts can access them if they need to.
+ Fix error log printout in `smtk.simple` API.
+ Have python test `addToScene()` method return pipeline objects.