remark-abbr: optionally expand first occurrence inline

[roxspring]

Given the markdown:

This plugin works on MDAST.

More stuff about MDAST.

*[MDAST]: Markdown Abstract Syntax Tree

Then, with options of {expandFirst: true}, the plugin would translate to the following:

Would translate to:

<p>This plugin works on Markdown Abstract Syntax Tree (<abbr title="Markdown Abstract Syntax Tree">MDAST</abbr>).</p>

<p>More stuff about <abbr title="Markdown Abstract Syntax Tree">MDAST</abbr>.</p>

Note that this is not quite as spec'd in #304 since the "(MDAST)" in the initial expansion also gets recursively expanded. This wasn't intentional, and I haven't spotted how to avoid it, but I'm not sure it's awful behaviour either!

Opening a WIP pull request to get feedback on behaviour and implementation. Assuming positive response I'll update with documentation of the new functionality in README.md.

Closes #304

[roxspring]

Addressed @houndci-bot complaints.

Not clear whether the @traviscibot issues are introduced by my code changes - advice welcome!

[vhf]

@roxspring Looks good to me, that's definitely a useful feature! 👍

Please go ahead with the README update, I'll fix the failing tests (not your fault, no idea why cyrillic tests suddenly fail).
Edited: fixed the CI, please rebase on master

[vhf]

Thanks, merged via 4915e3b

I'll work on a release next week and will ping you here once released

[vhf]

@roxspring Here we go https://www.npmjs.com/package/remark-abbr/v/1.3.0 :)