(struct otf_list): Delete it.

(struct otf_list): Delete it.
(otf_list): Make it a lisp variable..
(otf_open): Use lispy otf_list.
(generate_otf_features): Renamed from parse_gsub_gpos_spec.
(check_otf_features): New function.
(font_otf_DeviceTable, font_otf_ValueRecord, font_otf_Anchor): New
functinos.
(font_drive_otf): New function merging font_otf_gsub and
font_otf_gpos.
(font_open_for_lface): New arg spec.  Change argument order.
(font_load_for_face): Adjusted for the change of
font_open_for_lface.
(Ffont_drive_otf): New function merging Ffont_otf_gsub and
Ffont_otf_gpos.
(syms_of_font): Staticpro otf_list.  Delete defsubr of
Sfont_otf_gsub and Sfont_otf_gpos.  Defsubr Sfont_drive_otf.