Falcon -> misc updates

[Steffen Möller <steffen_moeller@gmx.de>]

Hello,

with python3-networkx 2.5 the previously reported FTBFS is done. I am
just cowbuilding that monster again and will then team-upload.

Concerning falcon I transitioned everything (except for the module
declaration) to Python3. The nim code is now compatible with version 1.2
of nim. Especially that strings are no longer allowed to be nil rather
bit the code hard. I just pushed this all, so I don't lose these
changes, and also happily pass the finalisation of the package in other
hands. Should be these Python modules only ...

What we should really do so is to feed these changes back to upstream.

Steffen