Add toc config

[ficd0]

Added config option code_action.toc.include which is a list of integers. This is
the new default:

[code_action]
# Enable/disable "Table of Contents" code action
toc.enable = true
# Heading levels to include when generating a Table of Contents
toc.include = [1, 2, 3, 4, 5, 6]

These are the heading levels that will be included when generating a Table of
Contents. Keeping the default setting results in identical behavior to before.
However, changing the array allows us to exclude certain levels from the TOC.

I updated tests accordingly. This PR partially implements #91.

Asciicast demo available:

[artempyanykh]

This is great! Thanks for the contribution @ficd0!

The change looks good to me, modulo a few suggested improvements. Let me know if you want to address those.

[ficd0]

I'm happy to address them, thanks for the helpful review comments. I'll mark ping you here when it's ready for review. 🙂

[ficd0]

@artempyanykh ready for review, thanks for all the guidance! I have some experience with OCaml but it's my first time programming in F#

[artempyanykh]

Thanks for the contribution @ficd0!

[ficd0]

Thanks for the merge and for fixing my mistakes in the next commit. I'm too used to 1. Ocaml syntax for type constructors like int array and 2. The ocaml compiler yelling at me for unused bindings like in Rust.

Since F# allows type cons syntax as well as cons<type>, it really throws me off. Is it possible to get the linter to point these out? Same with unused bindings?

P.S. getting my development environment set up and figuring out how to run tests, formatting etc. Was a bit challenging. I think some contributor documentation would be super helpful for new contributors!

[artempyanykh]

@ficd0 no worries at all, appreciate the contribution! Agreed that contributor's guide would be helpful.
On the linters side, I found tooling somewhat lacking, sadly. I'll try to find time to give it another go in case there were improvements to fsharplint and/or some compiler flags to yell.