neon: 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