Implement --pid

[aersam]

Hi guys

Thanks for having created granian, it's a great thing!

There's of course always potential for improvement, here's something I miss from gunicorn:

• In gunicorn you can pass --pid which will write the gunicorn's pid (not the workers) into a simple file
• Using that PID you can then send signals to the Main process, see https://docs.gunicorn.org/en/stable/signals.html Most important one is probably HUP which will do a restart of the workers, which is very nice

Not sure I find the time to implement this, especially as I'm not a UNIX pro, but I could give it a try if no one wants to do this

[gi0baro]

Just to clarify: Granian already supports HUP signal to gracefully restart workers.

The --pid option sounds legit and easy to implement, targeting this for next minor.

[stefins]

I can work on this!