Fuzz test scrypt implementations against each other (good input)

Real fuzzing with bad input is TODO.
First stab at fuzzing bad inputs

No type changes, yet.
Compare type of exception
Fuzz bytestrings
Use 64-bit math in pylibsodium_salsa

Over 10% faster on python3, less on python2.

(2x as fast on pypy, but still much slower than pure python.)
Fuzz bad argtypes
Use unittest for running fuzz tests
Merge branch 'fuzz'

Small fuzz testing program for testing the various scrypt implementations.