Publish webfont to npm package registries

[alerque]

This is a follow up issue to discussions in #363, #365, and #362. Since actually doing this will be a discrete step from generating the webfonts I'm opening this issue to track when it is actually done.

Consider one or both of npmjs.org and GitHub's own package registry. Now that these are both owned by GitHub and gradually merging it may make senese to only use one, but at this ponit I don't know — whatever it takes so that adding a version specific Libertinus webfont as a dependency by adding it to a project's package.json is an easy step...

See also theleagueof/fontship#88