Add tags or comment to rules

[tweksteen]

I am writing a daemon to manage rules generated by system events (similar to what is described in https://usbguard.github.io/blog/2017/Screen-Locking). Some of the rules have different origins and I'd like to easily be able to query rules matching an origin. This could be in the form of a tag (arbitrary string) associated with the rule. Looking around, iptables implements a similar idea with the comments option (--comment).

I'm happy to follow up with the implementation, I'd like first some feedback on the desired approach.

[tweksteen]

This was merged in #293. Closing.