The source project of this merge request has been removed.
Add a direction parameter to FT_GlyphSlot_Slant, support slant from top to bottom for chinese vertical layout
Normally slant from left to right. In this case, char direction and flow direction has a angle of 90 degree. In chinese vertical layout, the angle is 180 degree, so slant from top to bottom. MS Office(Word) and Taishan Office all support this feature.