arrow

ARROW-657: [C++/Python] Expose Tensor IPC in Python. Add equals method. Add pyarrow.create_memory_map/memory_map functions

This adds a `MemoryMappedFile::Create` C++ function for allocating new memory maps of a particular size, with a Python wrapper. I combined the Cython header declarations for the main libarrow libraries into a single pxd file.

I am also checking in some tests from ARROW-718 that got left off the patch.

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #483 from wesm/ARROW-657 and squashes the following commits:

a5d2f00 [Wes McKinney] More readable cinit post refactor
fbf438d [Wes McKinney] clang-format
4024c22 [Wes McKinney] Fix MSVC issues, use slower SetBitTo implementation that doesn't have compiler warning
7847d0f [Wes McKinney] Make file names unique
994b83d [Wes McKinney] Try to fix MSVC
25cfc83 [Wes McKinney] Expose Tensor IPC in Python. Add equals method. Add create_memory_map function and memory_map factory