Release the GIL in the new back-end to allow multi-threads computation.

Doc for the new type of profiling added.

Testing the output shape

Fix get_conv_output_shape for symbolic input

one ctx async 3.349727
two ctx async 1.713157
two ctx, 2 fct async 1.717468
two ctx, 2 fct with transfer 3.635517
two ctx, 2 fct async, 2 threads 1.731599
two ctx, 2 fct with transfer, 2 threads 2.071597

Fix call to gpu_from_host

Fix not using context_name in local_gpu_elemwise

Factoring inference of convolution output shape (continuation)

Fix #3190

Better error message.

Conv3d

Factoring inference of convolution output shape

Fixed error in doc

Fixes cl.exe not being seen on Windows

Port the speedup from #3163 to the new backend.

Enable cudnn for AbstractConv2d