[ literate ] Support typst in literate Idris

[buzden]

Description

Typst is relatively young typesetting system which aims to be as powerful as TeX while being lightweight more like Markdown and extensible by programmers with custom libraries (and tens of them are already around).

I personally use Pandoc Markdown + raw TeX insertions with Literate Idris for my papers and presentations, and I find this facinating, especially an ability to compile and run my slides and thus to check all the code on them during build of a PDF. I'd like to use typst too for that, but now compiler does not support it, which is not much a change.

So, I suggest to add the support for typst files. Also I made a small refactoring in a separate commit, and I tried to correct/extend existing literate Idris documentation.

Should this change go in the CHANGELOG?

• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG_NEXT.md (and potentially also
  CONTRIBUTORS.md).

[andrevidela]

@gallais are we waiting on something to merge?

[gallais]

Would be nice to have a test

[buzden]

I've added a test to the last commit