deploy/gh-pages: tidy output before deploy

[sidvishnoi]

So, the diff is easier to read, if any. Also, deployed output is easier to read with view-source
Will also play nice with #8

[sidvishnoi]

Help wanted: use prettier or html5-tidy?

Prettier: Easy to install and run. Creates awkward output many times (self-closing tags with trailing slash, tags with many attributes go multi-line awkwardly).
Tidy: A bit more difficult to install, updated less frequently. Formatting feels more natural.

[sidvishnoi]

Prettier with --html-whitespace-sensitivity=ignore seems nice, though it can have negative effect on layout and crawlers like reffy and specberus.

[marcoscaceres]

Maybe we should make this configurable (and default to html5 tidy).

[marcoscaceres]

Ran into wanting this today.... just just bumping for myself.

Maybe we can do another coding session for this in the coming month after TPAC?