Include CMU Serif, simplify CSS imports

This uses my new computer-modern package to make Computer Modern Serif available directly from Mafs.

This changes the CSS import in Mafs:

-@import "mafs/build/index.css";
+@import "mafs/core.css";
+@import "mafs/font.css";

font.css is optional. It just imports computer-modern/cmun-serif.css and sets the MafsView font.

One thing that might be handy in the future would be to subset the fonts to only have numbers and common characters, so that the browser doesn't have to load so much content just to show axes.

stevenpetryk / mafs

Include CMU Serif, simplify CSS imports #72