Various documentation mark-up fixes to make the output more
consistent in general and also make AsciiDoctor (an alternative
formatter) happier.
* jk/asciidoc-markup-fix:
doc: convert AsciiDoc {?foo} to ifdef::foo[]
doc: put example URLs and emails inside literal backticks
doc: drop backslash quoting of some curly braces
doc: convert \--option to --option
doc/add: reformat `--edit` option
doc: fix length of underlined section-title
doc: fix hanging "+"-continuation
doc: fix unquoted use of "{type}"
doc: fix misrendering due to `single quote'
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