* Add shared lib target for GPU version.

* Dynamically link tutorial examples.

* Add shared lib to clean target in GPU Makefile.

* Add clean target to tutorial examples Makefile.

* Minor modifications to tutorial GPU examples.

* Remove transitional print import.

* Add example for multiple GPUs in python.

* Add example on GPU in C++.

* Add example on multiple GPUs in C++.

* Add IVFFlat example on GPU in python.

* Add Makefile for C++ tutorial examples.

* Add IVF index on GPU example in C++.

* moved most FAISS_ASSERT calls to C++ exceptions, and adjusted
  memory allocation to avoid mem leaks

* added an IndexIVFScalarQuantizer type that offers an
  intermediate compression between IVFFlat and IVFPQ

* support removal of indices in IndexIDMap / IndexFlat combination

* various fixes in GPU code

  memory allocation to avoid mem leaks

* added an IndexIVFScalarQuantizer type that offers an
  intermediate compression between IVFFlat and IVFPQ

* support removal of indices in IndexIDMap / IndexFlat combination

* various fixes in GPU code