fixes #148 + test case
Merge pull request #163 from reaperhulk/fix-bug-148

Return proper string type from hexdigest in py2/3
Merge pull request #155 from reaperhulk/hmac-vectors

HMAC test vectors
Remove a dangling reference to Read The Docs.
Merge pull request #164 from dreid/dangling-rtd-reference

Remove a dangling reference to Read The Docs.
hmac support