Makefile
Introduce 'request'

'request' is a combination of sending and receiving, in order to avoid
sending signals and forgetting to wait for an answer, potentially
starving the server thread.
Development stage: alpha
Server always responds to incoming requests
Check permission on incoming requests
CMD arg parser (optparse-applicative) skeleton
Constrained argument readers (e.g. "> 0")
Arg parser works
Make verbosity parameter case-insensitive
Fix mixup of min/max neighbour in arg parser