pxssh prompt synchronization and new parameters

Updated prompt synchronization to improve to have tunable best/worst case performance.


Updated login method with a few helpful parameters:

quite - trims out all except for the raw session data (useful for TCP forwards)

sync_multiplier - tunes the best/worst case performance of the prompt synchronization. Default of 1.0 results in 500ms best case, 12 second worst case.

check_local_ip - True (default) to verify the host key when performing a login to localhost, False to skip key verification for localhost (also useful for TCP forwards)