Merge pull request #124 from reaperhulk/hash-saga-sha2

Hash Saga Part 4 (SHA2 support)
SHA2 family support
ripemd160 support + long string hash test

* Note that the long string hash test for RIPEMD160 adds a vector in the
  test. You can verify this vector (for b"a" * 1000000) on the RIPE
  homepage: http://homes.esat.kuleuven.be/~bosselae/ripemd160.html