Perpetrate SVG on the codebase

Well, parts of it.
We can have black and white SVG only.
I think it's currently buggy.

I figure we should probably be able to actually parse a document format.
And SVG, despite being XML, seems like the least terrible.

Using pugixml for XML parsing and horrible string tokenising because
SVG is not really a DOM language because of the "d" attribute (-_-)

Did I mention it was the least terrible?

Also, there seem to be lots and lots of bugs with things,
including Quadtree rendering of Beziers and actually just  GPU rendering of more than one
Bezier in general.

Also I compiled atril without zoom limits but it crashes
due to things not related to precision. So we're beating atril I guess. Woo!