Initial (incomplete) support for EDUPUB

 * Import schemas from @mattgarrish
 * custom OPF checks based on the `edupub` `dc:type` value
 * custom XHTML checks based on the `edupub` `dc:type` value
Adapt JS regex to fix a hanging issue
Merge pull request #435 from IDPF/feature/edupub

Initial (incomplete) support for EDUPUB