New top-level mode for LaTeX, HTML, or Org-mode output

[mahrud]

In Macaulay2/M2-emacs#79 I suggested a new top-level mode for producing LaTeX output which can be previewed inline using Emacs (or vscode).

This made me wonder why we don't have some obvious top-level modes:

1. A mode which produces a truncated html file, in such a way that you can open the partially written html file in a browser for a cheap WebApp replica, where you need to refresh to load the rest of the page after every command. There's tons of ways to improve this, e.g. obviously syntax highlighting, a navbar at the top of the page, parsing of positions into links, auto-update using javascript, incremental loading, perhaps even a basic http server running in M2 to serve the output via 127.0.0.1 in this mode to a single browser (maybe with json?) and handle interrupts that way. (Side note: can an M2 thread interrupt a running command in the main thread?)
2. A mode which produces an essentially complete LaTeX source file, basically consisting of input lines in \verbatim followed by the LaTeX output line.
3. A mode which produces Org-mode. Even better would be if it was reproducible, i.e. you could grab the org-mode output of an M2 session and rerun/update everything in it like Jupyter.
4. A mode which produces Markdown for viewing in capable viewers.

I think @d-torrance has a usable version of 3 already, but I think 1 above is the one I'm most interested in because its a lot simpler to use locally than either Jupyter or the WebApp.