4dir is like facedir, but only for 4 horizontal directions: NESW. It is identical in behavior to facedir otherwise. The reason why game makers would want to use this over facedir is 1) simplicity and 2) you get 6 free bits.
It can be used for things like chests and furnaces and you don't need or want them to "flip them on the side" (like you could with facedir).
color4dir is like colorfacedir, but you get 64 colors instead of only 8.
set_sky: New feature, keep note about the old syntax
get_us_time: Document overflow
localplayer: Document "nil" behaviour before initialization
collision_box: Safe limit of "1.45"
