Option lists and maps are specified using separate arguments, avoiding
the need for additional escaping of their separator and reusing the
existing command line spliting logic instead.
As discussed on #2087, this should make it much easier to work with
list options, and make the general option system feel cleaner.
This commit allows setting the `commands` flag to the `debug` option, in
order to have the engine write on the *debug* buffer the commands that are
being executed, along with their arguments.
