Add support for Raku packages

[pombredanne]

These are called distributions.

See

• https://360.zef.pm/
• https://raku.land/zef:lizmat/PURL <- nice PURL implementation
• https://github.com/ugexe/zef

Some prep and design needed.

[pombredanne]

@lizmat FYI :) ... we surely will need your review in the near future!

[lizmat]

Thanks for the nudge: my focus has been on getting the Raku Foundation off the ground, see https://dev.to/lizmat/a-year-later-a-trf-1lh0 .

I hope to be able to get into this in the coming weeks.