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ARROW-1782: [Python] Add pyarrow.compress, decompress APIs

This enables bytes, Buffer, or buffer-like objects to be compressed either to PyBytes or `pyarrow.Buffer`. Wanted some feedback on the API (argument names, etc.). The compression API in Arrow in general requires knowing the size of the decompressed data, but some compressors (like Snappy) are able to tell you how big the result will be based only on the input buffer

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

Closes #1345 from wesm/ARROW-1782 and squashes the following commits:

f297103b [Wes McKinney] More assertions, nicer error message when decompressed size not passed
7cd0fdb7 [Wes McKinney] Tests for compress/decompress passing
38480411 [Wes McKinney] Draft implementation of pyarrow.decompress
29b82dca [Wes McKinney] Docstring for pyarrow.decompress
2eeaf9a8 [Wes McKinney] Expose ResizableBuffer as Python class, test
6968be3f [Wes McKinney] Work on compress/decompress methods