Vectors ToString and Clamp

Added ToString representation for Vector2, Vector3, Vector4 and Rectangle. I use this all the time to debug positions, bounding boxes, etc...

Also added Clamp methods for Vector2, Vector3 and Vector4.

There's other Clamp methods that I didn't implement because I couldn't figure out passing by reference...

TODO: Format numbers a little better, right now it shows many, many decimal numbers if number is not integer. Could use toFixed or toPrecision but it'll add zeroes to an integer...

By the way, this is my first ever pull request. I hope I'm doing everything right.