mmh3 not 64-bit ready

[pitrou]

mmh3 cannot hash data larger than 2**31 bytes:

>>> import mmh3
>>> import numpy as np
>>> a = np.zeros(2**30, dtype=np.int8)
>>> mmh3.hash_bytes(a)
b"O\xc5\xf1\xf2\x80';s\x1b\xddc\xa1E\x8d\xe3r"
>>> a = np.zeros(2**32, dtype=np.int8)
>>> mmh3.hash_bytes(a)
Traceback (most recent call last):
  File "<ipython-input-9-918a38167947>", line 1, in <module>
    mmh3.hash_bytes(a)
OverflowError: size does not fit in an int

The solution is to either use the s* code instead of s# in PyArg_ParseTuple(), or define the PY_SSIZET_CLEAN macro and change size fields from int to Py_ssize_t. See https://docs.python.org/2.7/c-api/arg.html . I can also make a PR if you want.

Also, there's no test suite?

[hajimes]

Hi pitrou. Thank you so much for your suggestion and providing concrete solutions to improve the code. I just updated this library to incorporate your suggestion. Feel free to ask me if you still need other features.