Groups are a thing and sort of have a bounding box now

That was what I forgot in the last commit; I added "GROUP".

So, the idea is that GROUP can be used to shade a path.
Maybe. Eventually.

Or, it could just be used to make quad tree magic easier (?)

Or it could do both! (Since you can pretty easily just turn off the shading...
 but we're getting ahead of ourselves a bit there)

Or, if it gets given a name, then it can be used to implement the <use> SVG tag.
And then we can allow recursion (which regular SVG doesn't support).

Wouldn't it be nice...