WIP - Basic webmention support

[vikanezrimaya]

Related Issue
Was discussed in email with repo owner. [Angelo: Issue #40 opened to track this]

Issue mentioned in post: https://fireburn.ru/post/why-my-site-looks-as-it-does/

Dependency Changes
Added jQuery. Can be removed if someone bothers to port comment section in single.html to vanilla JS.

Testing

• Built and tested to work on a standalone Hugo site
• Built and tested to work in the Hugo Theme Gallery demo site (link)
• Tested with browser's responsive-design tools
• Tested in production

Additional context
Like buttons are not included because:

1. More JS would be needed (one JS per post)
2. The design is not polished yet

[AngeloStavrow]

Thanks so much for submitting this PR! I've opened #40 for some additional tracking and will start reviewing your changes.

[AngeloStavrow]

I've added WIP ("Work In Progress") to signal that this isn't yet ready to merge.

[AngeloStavrow]

So this is taking a lot longer than I expected, as I learn about the intricacies of webmentions myself.

One thing that I'm wondering is if it's worth downloading the whole jQuery library if we're only really interested in $.getJson() — most modern browsers support ES6's fetch(), which might be a little more lightweight (IE doesn't support it, so we might need a polypill there).

[vikanezrimaya]

One thing that I'm wondering is if it's worth downloading the whole jQuery library if we're only really interested in `$.getJson()` — most modern browsers support ES6's [`fetch()`](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch), which might be a little more lightweight (IE doesn't support it, so we might need a polypill there).

See [youmightnotneedjquery.com](http://youmightnotneedjquery.com/) for some tips on how to replace jQuery and even remain compatible with some reasonably recent versions of IE. But seriously, I think alsmot nobody uses IE anymore. Also CDN requests should be cached in browsers, if I understand it properly, so I don't think jQuery requirement should be a problem for most users. But don't count on my knowledge for this since I'm not sure.

[dpflug]

About 88% of users can use fetch(). According to that, IE is still in use by ~2.5% of users.