Please consider to allow application/x-font-ttf as a CoreMediaType as well (refs #443)

This came to my mind when reading the changelog and seeing #443, I had to think about w3c/epubcheck#586:

However, it's declared as application/x-font-ttf in the content.opf file which may seem wrong, but it's still the correct mime-type for OpenType with TrueType outlines.

There are OpenType fonts with TrueType outlines for whoch the mediatype application/x-font-ttf is perfectly valid and widely recognized. Please considder adding it to EPUB 3.1