Mostly mechanical: `markdownlint-cli2 --fix` over the directories the md
linter covers (blank lines around fences and lists, list indentation, bare
URLs wrapped in angle brackets, stray spaces inside code spans).
A few spots needed to be fixed by hand because they were malformed in the
first place: reference links left dangling by the RST conversion in
ipc/docs/ipdl.md and devtools/docs/user/debugger-api/index.md, an `{image}`
directive whose options had escaped the fence in
docs/contributing/debugging/capturing_minidump.md, and text where a literal
asterisk or underscore was being parsed as emphasis.
Differential Revision: https://phabricator.services.mozilla.com/D315001
Sylvestre Ledru
e173c24599