support for tikZ commutive diagrams

[cindywu]

Brendan F. asked me and Denny if we support tikZ. Jelly does not support tikZ, but at some point I think we should.

tikzcd-editor: https://tikzcd.yichuanshen.de/

I am pretty unfamiliar with tikZ, but my current understanding is it is a package to draw diagrams in LaTeX.

Example diagram using tikZ:

http://ctan.math.washington.edu/tex-archive/graphics/pgf/contrib/tikz-cd/tikz-cd-doc.pdf