make cudamat pip installable.
python3 compatibility, doc updates.
keep learn submodule functions separate.
Create custom nvcc compiler extension.
continue when LD_LIBRARY_PATH not set.
Use nvcc for linking to avoid CUDA library lookup
Allow NVCCFLAGS to customize compiler invocations similar to CFLAGS, CXXFLAGS etc.
Merge pull request #1 from f0k/more-setuptools

Use nvcc for linking
Merge pull request #31 from NervanaSystems/pip_package

make cudamat pip installable.