Relicensing to GPL-3.0-or-later — contributor consent needed

fresh is moving from GPL-2.0 to GPL-3.0-or-later.

Why: some of our dependencies are Apache-2.0, which is incompatible with GPL-2.0. GPL-3.0 fixes that.

GPL-2.0 has no "or later" clause, so I can't do this without your OK.

If your name is below, please reply with this line:

I license my past and future contributions to fresh under GPL-3.0-or-later, and agree they may be relicensed at the maintainer's discretion in the future.

Contributors with code still in the tree

@asukaminato0721 @NihilDigit @PavelLoparev @Agrejus @theogravity @masmu @maupin @1612elphi @Nandaleio @aymuos15 @adamnemecek @56steve @Crocmagnon @rishiyaduwanshi @ttenneb @can2049 @bacteriafield @atirna @radiorambo @ianyepan @ko3n1g @peanball @richiehowelll @sfjohansson @mandolyte @mommysgoodpuppy @yz7vx @dwt @masak1yu @Yousa-Mirage @mokurin000 @xoxorwr @ci4ic4 @casibbald @Smotrov @wellorbetter @pm100 @atk @fdefilippo @jasonIWU @Tyooughtul

Future contributions

CONTRIBUTING.md and a PR template now carry the same terms, so this doesn't need to happen again.

Thanks!