Add target to generate webfont only package suitable for publishing to NPM

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Add a make target that will generate a package that bundles webfont builds of a font project and any necessary CSS with suitable meta generated from what we already know about a project in a form suitable for submission to an NPM package registry.

Such a package should make it easy to include as a dependency for many web projects that use npm to manage dependencies already to add a font as a dependency with good versioning and easy integration into a site publishing workflow.

I know that we'll need to generate a package.json file, but I don't know what the best file layout should be for such a webfont package. If anybody knows off the top of their head or has examples of specific font projects that have done this well already comments would be much appreciated.

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See also fontsource.