Add support for reStructuredText

[klein0r]

Comments are defined like this:

..
    _This: is a comment!

..
    [and] this!

..
    this:: too!

..
    |even| this:: !

Additionally, support for https://www.sphinx-doc.org/en/master/usage/extensions/todo.html would be awesome

.. todo::
     This is a todo

[alstr]

Interesting, thanks for the suggestion! It would definitely be good to add this; PR requests are always welcome for new languages, and they're relatively easy to do. This does look a little more complicated than the standard comment syntax. For one, at the moment if the comment delimiter is not on the same line as the 'todo' keyword/title, it won't get picked up, but that is something I am hoping to improve.

[alstr]

I've done some experimentation and the challenges to adding this at the moment are:

• The lowercase todo (added support in latest commit)
• The double colon after todo (at the moment it thinks the second colon is the title)
• The fact that the formatting is somewhat unique; it isn't like a normal line comment as there is no comment delimiter on the second line, but it isn't a block comment as there's no closing tag.

The second one is an easy fix; the third is a bit more involved.

[silopolis]

We'd surely be a bunch to welcome this addition!
Thanks for taking care of it :)