Track and/or limit site size

[nathanielknight]

This site is Pest's public face, and currently loads quickly and performs well. In an effort to keep it that way, we should be mindful about how much extra JavaScript, CSS, etc. we ask Pest's users (or prospective users) to download.

"Historical" site sizes can be checked by checking out and building old versions of the site. Alternatively, if we can set up our publishing process to use Releases, we can save each build and see site size trivially.

If we want to set hard limits to the site size, we might consider adopting a tool like bundlesize to catch any unexpectedly large changes in site size.