Add folding

[ldez]

Reported from asciidoctor/atom-language-asciidoc#7, originally open by @antonmoiseev

[sanmai-NL]

What can we do to implement such a feature in some form soon, despite the limitations of Atom (discussed in asciidoctor/atom-language-asciidoc#7)?

[mojavelinux]

The upstream issue seems to be atom/first-mate#48.

Until then, perhaps we can define custom folds using this plugin: https://atom.io/packages/custom-folds

[ojn]

When I was using Atom I had adopted markdown-folder fom tshort. As far as I can tell, it still works and has been working in a few latest Atom releases. I think Atom had changed how they do folding. Tshort should not had deprecated his package because "the old way" to do the folding works nicely.

I will try to clean it up (my fork of it) - asciidoc-folds.
I have never published Atom packages so if anyone could assist me I would be happy, even better if it can be absorbed to atom-asciidoc-assistant so that it finds someone to maintain it because I don't think I would be switching back to Atom.