Add FC_FONT_WRAPPER
Currently detects only SFNT wrappers:
- WOFF: if it is FreeType says it is an SFNT font the file starts with wOFF tag
- WOFF2: the same but tag is wOF2
- SFNT: for any other SFNT font (which helps distinguishing standalone CFF fonts from CFF in SFNT aka OTF)
Fixes #375 (closed)