Reduce the surface of the primitive hash interface.  Add more interfaces, drop direct hashlib compatibility.
Ignore abstractproperty.
Fix python3 compatibility and pep8
Merge branch 'master' into primitive-hashes
Update documentation
Fix python3 compat for the hash_test.
Enforce that Hash takes a HashAlgorithm instance.
Inline _copy_ctx
Improve Hash documentation.
Merge pull request #200 from dreid/primitive-hashes

[WIP] Reduce the surface of the primitive hash interface.
fixed rendering
Document how this returns bytes
Merge pull request #210 from alex/docs-fix

fixed rendering
For example
better english
Strip down the HMAC interface to be HashContext.
Remove unused import.
Enforce HMAC taking an instance of HashAlgorithm
Update documentation
ARC4 vectors from RFC 6229 reformatted for NIST loader