Added functionality and test.
Merge pull request #49 from defyrlt/feature/custom_json_encoder

Custom JSON Encoder
Bump up version for release
Removed some unnecessary references to PyCrypto's Crypto.Hash functions in the ECDSA code since it uses hashlib functions anyways. This removes an ECDSA dependency on PyCrypto.
Fixed tests so that they will still run without failure when
dependencies (PyCrypto, ecdsa) are missing. (Tests are skipped if
libraries are not present.)
Added reference to unittest2 so that Python 2.6 can use skipIf
Modified RSA algorithms to use cryptography library instead of PyCrypto