Rewrite of the layer between Python and C++ to remove global memory constraints.

• Major rewrite of the layer between Python and C++, which was previously written using the numpy C++ API, and now is written in cython.
• The C++ that remains has been cleaned up a bit and formatted.
• The major functionality change is that global memory is no longer used, so reserve_num_graphs no longer needs to be called and Network objects can be created and destroyed at the user's pleasure.
• The change in global memory made the calls to init_pois no longer necessary. Then, that method has been removed and the max_items and max_distance parameters were relocated in the set_pois call.
• The nearest neighbor queries are now resolved with Scipy instead of libANN. That removed additional global memory.