ENH: new text class for inline color changes

This would be nice to have for my upcoming experiment: since I'm using color cues, I want to change color inline during the instructional text to make the explanations clearer. I fully acknowledge that pyglet's handling of formatted text is buggy, but it seems to be stable as long as all you change is the color (which is all I need to do) and not the typeface or size.
...and I'd almost rather just work with attributed text. If it just adds capabilities (or only adds very few restrictions), then it's worth just *always* having text be attributed.