Support farmhash for bytes-like objects

[jcdong98]

In the current version,

• farmhash does not support bytes in Python 3.
  For example, farmhash.hash64(b'123') will lead to TypeError: argument 1 must be str, not bytes.
• It does not support strings containing embedded nulls as well.
  farmhash.hash64('\x00') will cause ValueError: embedded null character.

This PR enables the functionality to deal with bytes-like objects and strings containing embedded nulls. After this PR is merged, we can call farmhash functions as follows without error.

farmhash.hash64('abc')  # 2640714258260161385
farmhash.hash64(b'abc')  # 2640714258260161385
farmhash.hash64('\x00')  # 13718060045003475796
farmhash.hash64(b'\x00')  # 13718060045003475796