cuDNN acceleration

Caffe + cuDNN is an NVIDIA-Caffe collaboration for deep learning. 
[cuDNN](https://developer.nvidia.com/cudnn) is an acceleration library for deep network operations with drop-in integration to Caffe.
It is a free library downloadable with CUDA developer registration.
This combination is the fastest public framework for deep learning with overall model speedups of 1.2-1.5x and layer-wise speedups of 1.2-3x over standard Caffe.

Check out the cuDNN site and [Caffe's latest roast slides](https://docs.google.com/presentation/d/1mlei57vB5-7_rFVMOOoP57pvCn3kQo3LTze4cEecLxw/edit#slide=id.g3aede17a4_0107).

This PR will be updated shortly with an announcement in full detail.