Add Python3 support for the client-side.

Also fixed a bug/worked around an issue in the ecdsa package. VerifyingKey.from_pem() doesn't take a hash function argument, so I'm specifying it in verify().

I err'd on the side of caution in regards to encoding things. Everything should still work under Python2 as well.
Merge pull request #1 from paxswill/py3k-fixes

Add Python3 support for the client-side.