Editorial: Update note markup/markdown and styling

[inexorabletash]

Using the note: ... markdown, Bikeshed produces nicely styled notes with a "NOTE:" prefix automagically generated. This source was not using that, so not getting the nice prefix. Fix that!

• <aside> was used for notes, examples, and advisements, but it's not a block element. Just use <div>.
• For notes, use NOTE: markdown where possible (single paragraphs)
• Otherwise, add "NOTE:" manually as a span, class=marker
• For a handful of cases where a note follows an algorithm and references variables within the algorithm, scooch the note inside the algorithm's containing div so that it is autolinked.
• Remove a stray unbalanced </div>

See https://github.com/speced/bikeshed/issues/2562 for context.

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[inexorabletash]

Hey @marcoscaceres - I know bikeshed isn't your normal jam, but maybe you could take a look at this?

(Not urgent at all.)

[inexorabletash]

@a-sully - could I trouble you for a review of this too? Thanks!

[inexorabletash]

Thanks @a-sully !