Python 3 support, persistent RNN kernels, and improvements to dataloader, convolutional kernels and docs.

• Python2/Python3 compatibility [#191]
• Support for Pascal GPUs
• Persistent RNN kernels [#262]
• Dataloader enhancements (audio loader with examples)
• HDF5 file data iterator
• Convolution kernel improvements
• API documentation improvements [#234, #244, #263]
• Cache directory cleanup
• Reorganization of all unit tests
• Bug fixes [#182, #183, #231, #241, #252, #253, #257, #259, #267]