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
Merge pull request #125 from reaperhulk/hash-saga-ripeness

Hash Saga Part 5 (RIPEMD160 support)