Pyro4

- corrected bogus space in worker thread name
- thread server can now be cleanly stopped with SIGINT / Ctrl-C on Windows
(if the selectors module is available which is also used by the multiplex server)
- the behavior of the NATPORT config item has been corrected to be in line with the API behavior of the Daemon:
if you leave this at 0 (the default), it will now correctly replicate the internal port number as NAT port
(instead of crashing with a configuration error)
- certs are now included in sdist archive so the ssl unit tests also run as intended
- now correctly checks for write access to the correct logfile location, instead of assuming the current directory

- fixed distributed-mandelbrot example to actually run multiple concurrent calculations.
- CI build process now using more modern Python versions.
- missing API method doc added on NameServer.count()

- serpent 1.27 required to avoid regression in previous version
- fixed marshal serializer problem that prevented it to even call register() in the name server.
Its dumpsCall is now able to use the class_to_dict conversion for unmarshallable types
(in simple situations, not recursively). Previously, you would get a ValueError: unmarshallable object.
- msgpack, json and marshal serializers now understand how to serialize array.array the same way serpent already did

- include LICENSE file in distribution
- avoid decode error when dealing with memoryview annotations

- (source files: normalized line endings to LF)
- the -k command line option to supply a HMAC encryption key on the command line for the name server, nsc,
echoserver, flameserver and httpgateway tools is now deprecated (and will print a warning if used).
It is a security issue because the key used is plainly visible.
If you require proper security, use Pyro's 2-way SSL feature. Alternatively, set the HMAC key in the (new) environment
variable PYRO_HMAC_KEY if you still have to use it before launching the aforementioned tools.

- updated ``msgpack`` dependency (was ``msgpack-python`` but that name is now deprecated)
- fixed restart and force reload commands of the contrib/init.d/pyro4-nsd script, and changed its port binding
from 9999 back to 9090 which is Pyro's default.
- serpent 1.24 library now required to fix some api deprecation warnings when using Python 3.7 or newer.
- updated sphinx documentation theme