Lowdown requires a blank line before all preformatted blocks, or it doesn't
recognize them. `tools/md2man.sh` contained some ad-hoc efforts at fixing up
some locations where these required blank lines are absent from the output of
`tools/fromschema.py`, but it missed some. Instead of playing Whack-a-Mole, use
a blanket sed expression to ensure that a blank line precedes _every_ opening
```.
`esc_underscores(…)` in `tools/fromschema.py` did not work correctly on strings
containing an odd number of backticks, notably the ``` delimiters surrounding
preformatted text blocks. Specifically, it was dropping the last backtick since
none of the alternatives in the regex matched it. Add a new alternative that
matches a whole preformatted block as a single unit.
`output_member(…)` in `tools/fromschema.py` was passing each line of a member's
description through `esc_underscores(…)` individually, but that breaks
preformatted text blocks that are naturally multi-line and leads to mistakenly
escaping underscores inside such blocks. Rewrite the code to make use of the
`outputs(…)` utility function that joins all the provided lines together before
passing the whole text through `esc_underscores(…)`.
Drive-by fix a couple of flubbed preformatted blocks in schemas.
[ Added shellcheck suppression for md2man.sh --RR ]
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