This diff adds two functions to project 3d coordinates onto a 3d plane, to get 2d coordinates, essentially eliminating the plane's normal axis from the coordinates. This allows the use of 2d computations on the projected geometry which often makes things more straight forward and more efficient. For instance, you can check if a point is inside a polygon using these 2d projected coordinates.

The first function (map_to_plane_v2_v3v3) takes a 3d point and a normal, and gives you 2d coordinates with the normal axis factored out.

The second function (map_to_plane_axis_angle_v2_v3v3fl) is there for performance reasons. The first mapping function has to calculate the angle and axis of rotation between the given normal and a global z axis (i.e. {0, 0, 1}). When one has to project multiple points onto the same plane, using map_to_plane_axis_angle_v2_v3v3fl is recommended, which unlike the first one, directly takes the angle and axis I mentioned instead of computing them from the normal, thus saving those redundant computations for every point.