docs: Improve internal API documentation and update comment format to Yard

[jaredcwhite]

UPDATE: see #283

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Looking through the generated docs from Yard: https://rubydoc.info/gems/bridgetown-core/

Right now any useful information contained therein is very spotty and some files have no documentation whatsoever. We should prioritize incremental progress towards a fairly complete set of documentation around the core set of Bridgetown objects. Not as worried about ancillary objects like a string utility here or a tag there.

[jaredcwhite]

Definitely want to make sure we're providing comprehensive hover info for editors using https://solargraph.org

[jaredcwhite]

Also I'm assigning to you @ParamagicDev but obviously I can help out as well 😃

[KonnorRogers]

@jaredcwhite what branch would you like me to fork off of? Main?

[jaredcwhite]

@ParamagicDev yep, that's fine

[jaredcwhite]

Some improvements in #171, including switching YARD's text processing to Markdown format

[jaredcwhite]

Continuing to make progress in 0.20…still more to do though! 🤪