Change all XML comments to Liquid comments

[Rabadash8820]

XML comments (<!-- like this -->) still get rendered by Jekyll, which means they still get downloaded by site visitors. No reason to add those additional bytes (and anybody who cares can look at this source code anyway), so let's just convert them to the Liquid templating system's comments ({% comment %}like this {% endcomment %}. WAY more verbose, but better performance. 🤷‍♂️ Liquid v5 does have a tighter inline comment syntax, but as of this writing, Jekyll is still on Liquid v4 and there's no way to force it to use v5.