Headings/titles without closing sequence

[dumblob]

It's been already almost 2 years I came across DocOnce and since then I've realized, that it's kinda easy to convert existing documents from CommonMark to DocOnce (which was actually the primary motivation for #50 ). The only think I didn't manage to convert is my thinking and liking of one particular syntax choice which I consider tedious, unnecessary and cluttering.

Namely the need to end headings/titles with the same sequence of characters as at the beginning. I could not find a technical reason for this decision (each such heading paragraph is anyway already separated with a newline character before and after).

Would it be possible to make these closing sequences of characters optional? I.e. instead of:

===== My Title =====

allow just:

===== My Title

[KGHustad]

I think we could allow for the trailing =s to be optional.

If you want it fixed soon, feel free to make a pull request.

[dumblob]

I'm out of time, but I looked quickly into what everything would be probably affected. These are my observations:

1. Add mini test (probably one or two with skipped trailing = will be enough).

2. Add notes to specification & documentation.

3. Lines probably affected by the change (might change, but therefore the keywords next to them):

   • 921 syntax_check
   • 1583 1585 1597 1797 1896 1898 exercises
   • 2118 2122 2162 extract_individual_standalone_exercises
   • 3671 interpret_quiz_text
   • 4509 doconce2format

And I have a question based on the source code. Why does Doconce support 5 equal characters (=) at maximum? There is surely need for more "depth" in titles, subtitles, chapter titles, subchapter titles, etc.