* Add Python 3 support

* Update protobuf to 3.5 and pybind to 2.2.2

* Update test scripts to use python -m

* Change zip/xrange/import usages

* Remove file generated by

* Graph viz set up (#282)

* Include the Graph requirement, GraphViz` in docs.

* Provide information to the ONNX format model export.

* Ask the user to download Graphviz via the website instead of brew.

* Make test and build scripts compatible with python 2 & 3

* A WITH_PYTHON3 option was added to cmake.

* setup.py will detect runing version python, and setup up WITH_PYTHON3 environemnt variable before calling build.sh

* build.sh and test.sh will handle WITH_PYTHON3

* Fix pybind warning

* Pass WITH_PYTHON3 correctly

* Fix coding style

* Add six for Python 2 and 3 Compatibility

* Fix coding style