[raster] Keep only bottom y-turns.

This results in noticeable performance improvement.

* src/raster/ftraster.c (Insert_Y_Turns): All bottom y-turns are still
sorted and stored; only the maximum top y-turn is recorded now. The
function is renamed.
(End_Profile): Updated accordingly.
(Convert_Glyph): Reserve space for the top value.
1 file changed