release 4.44

• Behavior change: when the threadpool server is used and it runs out of worker threads, clients attempting to connect
  now get a connection error telling them that the server threadpool has to be increased.
  On python 3.2 and newer a short timeout is used for the case that in the meantime a connection becomes available.
• THREADPOOL_ALLOW_QUEUE config item added. Enables you to choose for the previous
  blocking behavior when the threadpool server can no longer accept new connections. Defaults to False.
  note: this is a temporary solution, in the next release a different threadpool implementation will be shipped
  for which this config item is no longer relevant. It will be removed again then.
• Fixed 'malformed string' error when a Python 2 client talks to a Python 3 server;
  proxy metadata and nameserver metadata tags are no longer returned as a set but as a list.
  (This problem occurs in the serpent serializer because of a problem with the underlying ast.literal_eval function
  across different python versions)
• improved multiplex server, now uses best available selector on your platform (kqueue, epoll, etc)
  This was done by using the 'selectors' module, on older pythons (<3.4)
  the backport 'selectors34' has been added as a new requirement.
• added selector property on the daemon (to expose the multiplexing selector if that servertype is used).
• Added Daemon.combine() which merges different daemons' request loops and lets you just run the 'master daemon' requestLoop
• fixed import and test problems with IronPython (it doesn't like the dill serializer either, like pypy)
• Improved security when comparing HMAC codes (against timing attacks)
• added 'diffie-hellman' example to shows a way to approach server-client agreement on a shared secret key
• a few IronPython releated changes regarding str/bytes to decrease the number of special cases