Add GetCollisionV

[danemadsen]

This is a function to get a vector for a collision which corresponds to how much the rectangles collide in each axis (relative to rec1).

For example:
Given a Rectangle a = { 10, 10, 20, 20 }
and Rectangle b = { 20, 10, 20, 20 }.

The resulting output of this function would be { 10, 0 }.
Which means there is a collision of 10 units in the x axis.

If you flipped the order of the rectangles so rec1 = b and rec2 = a the resulting output would be { -10, 0 }.

This is handy for collisions in 2D games where you may want a character to be blocked from moving in one axis but not in another without doing two collision checks.

[raysan5]

@danemadsen I think there is no need for an additional function, GetCollisionRec() can be used for that and managed in user side. Note that raylib priority is minimize API.