feature.feaを使って、GSUBの追加
font = TTFont(font_name)
feaLibBuilder.addOpenTypeFeatures(font, 'feature.fea')
font.save("fea_"+font_name)
feature.fea
languagesystem DFLT dflt;
languagesystem cyrl dflt;
languagesystem grek dflt;
languagesystem hani dflt;
languagesystem kana dflt;
languagesystem latn dflt;
feature vert {
substitute A by glyph12345;
substitute B by glyph12346;
} vert;
