Supporting YouTube and Twitter embeds

Swyxkit now supports YT and Twitter embeds, inspired by the Liquid tags from Dev.to, but extended to encourage dropping full URLs for futureproofing and markdown legibility.

The PR implementing this is sw-yx#41.

YouTube

Equivalent syntax:

• {% youtube https://www.youtube.com/watch?v=dQw4w9WgXcQ %}
• {% youtube dQw4w9WgXcQ %}

Result:

Twitter

Equivalent syntax:

• {% twitter https://twitter.com/swyx/status/1477408277994811393 %}
• {% twitter 1477408277994811393 %}

Result: