Animated sprites!

Mostly just added u_time and texcoords to the point shaders - I changed the point shape to square for this, could we   set that as a define?
These changes aren't necessary - if you just use the ```polygons``` mode as the base you are extending off of, it should just work, since that mode now supports textures, and renders points as a quad (I can show you POIs as an example). The ```points``` mode was mostly a test to try rendering non-rectangular shapes.

So I think you can drop all changes to this file.