Text has point_size and pos properties

And text always draws in that point size, even if inside a viewbox. There are two things to fix, see todo items:

* Is the pointsize correct like this?
* How to prevent recompilation on each draw?
This transform should be correct. In the `Text` object I normalize (or at least intend to normalize) the units of vertices such that it its local coordinate system, the font would be 1 pixel tall. This means that to get to point size, one would take the font size and divide by 72 to get to inches, then multiply by 92 *or whatever the actual dpi is* to get to pixels in height.

We should add a test image for `Text` -- my idea was to open Illustrator or Photoshop (or some other good graphics program), make a 1"x1" image, put some 48-pt (or so) text in the center, and output the result at 92 dpi. Then I'd use the `Text` visual in a 92x92px window and see if I got at least a similar result. WDYT?