*   Added an easy way to add and dynamically load user-defined ops
*   Built out a good suite of tests, things should break less!
*   Added `MetaGraphDef` which makes it easier to save graphs with metadata
*   Added assignments for "Deep Learning with TensorFlow" udacity course

## Bug Fixes and Other Changes

*   Added a versioning framework for `GraphDef`s to ensure compatibility
*   Enforced Python 3 compatibility