(FontLayoutCategory): New typedef.

(FontLayoutCategory): New typedef.
(FontLayoutStage): Type of the member `category' changed.
(struct _MFLT): Type of the member `coverage' changed.  New member
need_config and font_id.
(apply_otf_feature): New function.
(load_category_table): New arg FONT.  If FONT is non-NULL, call
apply_otf_feature.  Setup category->definition.
(ref_category_table): New macro.
(unref_category_table): New function.
(load_flt): Adjusted for the type change of category.
(free_flt_stage): New arg FLT.
(list_flt): Adjusted for the type change of category.
(run_stages): Adjusted for the type change of category.
(configure_category, configure_flt): New function.
(m17n_init_flt): Initialize mflt_iterate_otf_feature and
mflt_font_id to NULL.
(mflt_get): Skip the heading configured FLTs.
(mflt_find): Likewise.  If necessary, configure the found flt.
(mflt_run): Handle mflt_iterate_otf_feature and mflt_font_id.
Adjusted for the type change of category.
(mflt_iterate_otf_feature, mflt_font_id): New variable.