Pyro5

- finally ported over the unit test suite from Pyro4
- finally updated the documentation from Pyro4 to Pyro5 (there’s likely still some errors or omissions though)
- fixed regex lookup index error in nameserver
- the 4 custom class (un)register methods on the SerializerBase class are now also directly available in the api module

Fixed a silent error in the server when doing error handling (avoid calling getpeername() which may fail)
this issue could cause a method call to not being executed in a certain specific scenario.
(oneway call on MacOS when using unix domain sockets). Still, it's probably wise to upgrade as
this was a regression since version 5.8.

- fixed some circular import conflicts
- fixed empty nameserver host lookup issue

- added privilege-separation example
- added methodcall_error_handler to Daemon that allows you to provide a custom error handler, which is called when an exception occurs in the method call's user code
- introduced api.serve / server.serve as a replacement for the static class method Daemon.serveSimple
- fix possible race condition when creating instances with instancemode "single"
- introduced some more type hintings

- cython compatibility fix
- removed explicit version checks of dependencies such as serpent. This fixes crash error when dealing with prerelease versions that didn't match the pattern.

- fixed possible attribute error in proxy del method at interpreter shutdown
- gave the serialization example a clearer name 'custom-serialization'
- added NS_LOOKUP_DELAY config item and parameter to resolve()
to have an optional wait delay until a name becomes available in the nameserver
- added lookup() and yplookup() utility functions that implement this retry mechanism