Support display mode and commutative diagrams

[ScriptRaccoon]

With this PR we can render formulas in display mode by using the delimiters $$ ... $$. The katex documentation explains what display mode means.

In display mode we can also typeset commutative diagrams via the amscd package.

For example, this commutative diagram

can be typeset via:

$$\begin{CD} X @>{\mathrm{id}}>> X \\ @V{\mathrm{id}}VV @VV{f}V \\ X @>>{f}> Y \end{CD}$$

Diagrams

This PR has replaced all "manual" array diagrams with amscd diagrams. They look much better now.

Align environments

The align environment is also possible in display mode.

Display mode

This PR also uses display mode in several existing formulas (probably not all) where it was intended anyway.

[varkor]

(If you wanted to render more sophisticated diagrams, you could make use of quiver. I'd be happy to make some changes to make it more convenient to make use of in CatDat.)

[ScriptRaccoon]

(If you wanted to render more sophisticated diagrams, you could make use of quiver. I'd be happy to make some changes to make it more convenient to make use of in CatDat.)

Thanks! I will come back to this as soon as more complicated diagrams pop up. For now, they are quite simple, and amscd is sufficient. That might change in the future.