added public-key support to server mode, more docs
added public-key support to server mode (it can now verify a client signature)
and added a demo of that to the demo_server.py script (user_rsa_key). in the
process, cleaned up the API of PKey so that now it only has to know about
signing and verifying ssh2 blobs, and can be hashed and compared with other
keys (comparing & hashing only the public parts of the key). keys can also
be created from strings now too.
some more documentation and hiding private methods.
Robey Pointer