Vector.angle_signed(other)
for 2D vectors to get the clockwise angle between them.
in BLI math its called - angle_signed_v2v2()
shorthand for...
atan2f((v1[1] * v2[0]) - (v1[0] * v2[1]), dot_v2v2(v1, v2))
also corrects compile error in last commit.
* add BLI_rfindlink for reverse index lookup (used so bm.select_history[-1] doesn't have to loop the entire list twice).
* add bm.select_history.active so you can get the last selected item or None without having to check seq length.
