Change category symbols to use calligraphic font

[hmemcpy]

https://twitter.com/CarlHedgren/status/1036906077617618944

looks like \mathcal should do the trick: https://tex.stackexchange.com/questions/58098/what-are-all-the-font-styles-i-can-use-in-math-mode

All definitions are in https://github.com/hmemcpy/milewski-ctfp-pdf/blob/master/src/category.tex, so hopefully an easy change :)

[hmemcpy]

tip, looks like unicode-math overrides the default \mathcal font. To restore, add:

\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

to preamble

[hmemcpy]

This is put on hold for now.