Python versions posted

I have posted pure Python versions of Salsa20, ChaCha, BLAKE, and SHA-512 (which also supports SHA-384 and the new NIST algorithms SHA-512/256, and SHA-512/224).

Update (May   9): added Blowfish
Update (May 17): started a folder for Python3 conversions
Update (May 30): added a Python wrapper for C version of BLAKE