scrypt support

Created originally on Bitbucket by Anonymous

===== //(Imported from Google Code)//

SCrypt ([[http://www.tarsnap.com/scrypt.html|http://www.tarsnap.com/scrypt.html]]) is a key derivation function designed by Colin Percival; and is unique in that it is memory-hard as well as time-hard.

There is currently no password hash scheme based on scrypt, but one could be easily designed.

The main thing preventing support is that SCrypt's underlying KDF routines are not currently available at a python level through any third-party package, so Passlib would have to integrate a copy of the SCrypt source via a builtin C extension. Leading Passlib to the dark side of non-pure python, and the resulting build complications.