Update editors info

[sogaiu]

This PR is an attempt to address #222.

The initial content consists of:

• Creation of a separate editor section (broken out from being part of the "Modules and Libraries" section)
• An introductory paragraph explaining the content along with mentioning the "editors and tooling" discussion area in the Zulip Instance
• Changing the list of currently supported editors
  • Atom has been removed because it was sunset (the link wasn't leading anywhere useful AFAICT)
  • Helix and TIC-80 were added
  • The original ordering has been mostly preserved with new things being appended to the end of the list
• Each editor link [1] points to a page at this repository. Each such page there describes some supported features along with some relevant links.

This last change (pointing to a separate repository with descriptions) has the potential benefit of not having to update the list at janet-lang.org so frequently.

Don't know if folks are comfortable with this last point, but this is my initial proposal (^^;

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[1] To make it easy to see those links, here they are:

• Neovim
• Vim
• VSCode
• Emacs
• Sublime Text
• Kakoune
• TIC-80
• Helix

[sogaiu]

I've removed the draft status of this PR.