server: Added netascii mode

netascii is a silly mode from the 70's when you would use tftp over
telephone lines. So there is a reader now that a transpose your input
stream from octet (the mode with bytes of 8 bit each) to netascii, with
is byte allinged as well but doesn't use one of those bytes.

The docuementation states that this is important for 36 bit DEC machines
but some clients default to this mode. (some server might still be 36
bit machines from DEC)
Client: Reworked client instantiation

Client now has it's own type and can be instantiated multiple times with
different configurations
server: Cleaned up server code
cmd: cleaned command line interface

Server is started cleanly now, and it can use systemd socket activation.
server: Improved logging for control requests
server: Improved logging on request