file scheme not allowed in publications

[mattgarrish]

trafficstars

There should be a warning now if href attributes in the package document have absolute URLs that use the file scheme.

href is allowed on metadata link and manifest item elements.

See https://github.com/w3c/epub-specs/issues/1688

[mattgarrish]

This restriction has now been broadened and made more restrictive. file: URLs are not allowed anywhere in an epub publication.

See https://github.com/w3c/epub-specs/issues/2324