Render all embedded LaTeX images with lp/render

 I had been using a website to render these, but it didn't seem to
 handle some complex LaTeX very well, and I felt a little uncomfortable
 with the idea that if the site went down you couldn't see them any
 more, so I decided to add support for generating them myself to lp.scm.
 Here I make use of that support.
Exercise 1.13 (question only)