[Feature Request] Getter for sprite's pos and size in the atlas

[flamendless]

Something like:

local x, y, w, h = atlas:get_quad("duck")

[EngineerSmith]

I was going to add this function, but then I figured it would waste a few table calls for just doing atlas.quads["duck"]:getViewport() instead. Thanks for the suggestion, I'll throw it in for the sake of making it user friendly, while those who want to save those few cycles can inline it