A pure-Haskell SSH server library

#4port to RSA >= 2.0

The stackage cabal file has RSA ==2.1.0.1 as constraint, so it is unfortunate that ssh depends on < 1.3

The only API change in RSA I see is that ha_SHA1 has been renamed to hashSHA1. Renaming these functions makes ssh compile, but I get RSACipherRepOutOfRange in randomVerifyTest. I'm not sure if that is serious or not.