[BSv5] blocks/section row-col hierarchy fix

[chalin]

• Contributes to [BSv5] Row/col formatting breaks Docsy components #1466
• Contributes to Use Hugo's native support for processing HTML & markdown, not file extension testing #906
• Fixes the width/max-width of blocks/sections
• Section types are now switched! The type argument can be either container (the default) or row.
  This is a BREAKING CHANGE. I've updated the docs and the CHANGELOG.
• Whitespace cleanup
• Fixes a long-standing bug of a blank paragraph at the end of the About page, since before BSv5 changes

Preview: https://deploy-preview-1472--docsydocs.netlify.app/about

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Screenshots

Before

Notice the following problems (all of which are resolved by this PR):

• White space between the end of the last block and the footer
• Misformatting of bulleted lists
• Excessive width

After

[deining]

LGTM.

[LisaFC]

Looks great, thanks Patrice!

[chalin]

@LisaFC et al.: prior to deleting line 5 above, there was a _print version of the about page, which pretty much looked like the non-print version. With line 5 gone, we've lot the _print version of the About page. Is that ok with you? Given that the two pages are identical AFAICT.

[chalin]

For the record, this is what the _print page looked like (excerpt), before this PR was merged:

[LisaFC]

I don't think that's a problem, given that the page was exactly the same.