Xxhash

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- Change digest() from little-endian representation to big-endian representation of the integer digest.
This change breaks compatibility (digest() results are different).

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- Make this package hashlib-compliant

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- Update xxHash to r37

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- Improve: Check XXHnn_init() return value.
- Update xxHash to r36

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- Improve: Can now be built with Visual C++ Compiler.

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- New: XXH32 and XXH64 type, which support partially update.
- Fix: build under Python 3.4