Add license support to the resource pack generator CLI

[OpenBagTwo]

The resource pack generation script itself can accept both a license file and a string "license summary"

FoxNap/foxnap_rpg/pack_generator.py

Lines 100 to 108 in b5aa119

	license_summary : License or str, optional
	The usage summary to display on the resource pack loading screen. If using a
	License level enum, the level must be at least as restrictive as the most
	restrictively-licensed track. See notes. If None is provided, the license
	level will be set to the most permissive level appropriate for the included
	tracks.
	license_file : pathlike, optional
	The path to a license or credits file to include with the resource pack (for
	compliance with the terms of attribution-style or restricted use licenses)

to allow the user to make a redistributable resource pack that's less permissive than CC0, but the CLI currently provides no means of doing so.

(there are other pack customization options that could also be implemented but are less critical)

Fine-grained control is something that I'd prefer to save for if this generator ever gets a full-fat GUI, but for right now, at a bare minimum, the behavior should be that if a LICENSE.md or LICENSE.txt file is found in the music folder, that file gets copied over to the resource pack. I'd also want to enable explicit --license-file and --license-summary command-line flags.

This does not need to be done before the initial release