[DiapDealer]

A temporary input plugin to change the OPF package type from "1" to "2".
Will also workaround a Sigil bug that's triggered when an epub's opf file doesn't have an xml declaration.
(temporary because it will become unnecessary in the next version of Sigil)

It will change the package from "1.0" to "2.0" and will change any of the older "text/html" or "text/x-oeb1-document" media types on manifested items to "application/xhtml+xml".

It will add an xml declaration to opf files that don't have one.

Nothing else should be touched (including epub2s or epub3s).