Enable syntax highlight for code

[NamorNiradnug]

Maybe it was intentional to leave it black, but this would look nice.

[johanvx]

Yes, all the raw code text was intentionally set to black, for two reasons:

1. All the raw code text is black in the original document undergradmath.
2. I personally feel that for this document, syntax highlighting would be distracting—or rather, too much color would be distracting.

But I do agree that the distinction between the body text and the raw code text isn't very clear. Perhaps it could be improved by changing the font or the weight of the code.