Consider showing math symbols instead of some language constructions

[marat-rkh]

In Emacs mode for Coq (with company-coq), there is a special mode that shows math symbols instead of some language constructions, like lambdas, forall quantifier, etc.

With prettify-symbols-mode off:

With prettify-symbols-mode on:

We might try to add a similar feature to the plugin. Possible ways to do that include code foldings and Reader mode.

[sxhya]

I think that we might implement this feature similarly to how it is implemented in TexifyIDEA.