Switched hash functions from PyCrypto to hashlib.

There's a few advantages to this:

1) It's probably fast, OpenSSL, which typically backs hashlib, receives far
   more attention for optimizaitons than PyCrypto.
2) It's the first step to supporting PyPy, where PyCrypto doesn't run.
Merge remote-tracking branch 'alex/hashlib-hashes' into 295-int
Errything uses intersphinx to Python
Changelog, closes #295
Merge branch '295-int'