The keyword specifies how option works when specified multiple times:
- single: the last provided value replaces the earlier ones
- append: it supports being provided multiple times
- boolean: on/off values
- mutex: flag-like option that disable anoter flag
The 'gen.pl' script then outputs the proper and unified language for
each option's multi-use behavior in the generated man page.
The multi: header is requires in each .d file and will cause build error
if missing or set to an unknown value.
Closes#9759
The file format for each option now features a "Example:" header that
can provide one or more examples that get rendered appropriately in the
output. All options MUST have at least one example or gen.pl complains
at build-time.
This fix also does a few other minor format and consistency cleanups.
Closes#7654
