A pure-Haskell SSH server library

#10update for ghc 8.10

I believe making this build with GHC 8.10 would be a good next step. https://hub.darcs.net/simon/ssh-ghc810 has some unfinished work towards this. It builds, but most of SSH.hs is mostly commented out.

That is based on https://hub.darcs.net/simon/ssh, which as far as I know is the most up to date fork of ssh, and is the one used by darcs hub.

I'm not sure how these compare to the fork mentioned in https://hub.darcs.net/ganesh/ssh/issue/7.