Camera frustum check.

[Boyfinn]

I currently have my own implementation of this. But it would be great if a function for checking whether world coordinates are within a camera's frustum for both 2D and 3D cameras would be implemented into the library core.

[raysan5]

@Boyfinn I think that's a quite high-level feature that should reside on user-side but feel free to propose a Camera frustum check function for discussion.