IPv6 server bugfix, new Future waiters in Server API.

• bugfix: cannot bind to IPv6 address, closes issue #5
• enhancement: Futures waiter_connected, and waiter_closed added to
• server.
• change: TelSh.feed_slc merged into TelSh.feed_byte as slc_function
• keyword.
• change: TelnetServer.CONNECT_DEFERED class attribute renamed DEFERRED.
• Default value changed to 50ms from 100ms.
• enhancement: Default TelnetServer.PROMPT_IMMEDIATELY = False ensures
• prompt is not displayed until negotiation is considered final. It is
• no longer "aggressive".
• enhancement: TelnetServer.pause_writing and resume_writing callback
• wired.
• enhancement: TelSh.pause_writing and resume_writing methods added.