[cff] Add support for OpenType Collections (OTC).

* src/cff/cffload.c (cff_font_load): Separate subfont and face
index handling to load both pure CFFs with multiple subfonts and
OTCs (with multiple faces where each face holds exactly one
subfont).
* src/cff/cffobjs.c (cff_face_init): Updated.
3 files changed