Add Lua function: fadeToColor #33
Description
A basic Lua function to fade the screen to a specified color would be a nice and simple visual effect. The calling Lua coroutine should yield and be resumed only once the fade has completed (in the case of a standard "fade to black" for a scene cut, this would be the point where the screen is entirely black).
A complementary fade-in function to remove an existing fade would be useful to undo the effect.
Some of the FadeTransition code can be reused here so the fade doesn't need to be coded from scratch again.