NOTMUCH_OPT_INHERIT expects a notmuch_opt_desc_t * pointer in
output_var.
The "Unrecognized option" message was moved out of parse_option() to
not be emitted twice or when parsing a non-inherited option.
Previously, the cli parser was a little erratic in what errors it
reported and would fail silently in many cases (for example, when no
argument was passed to an integer option). This was particularly
annoying as the user could not (easily) tell whether the command
failed or just there were no search results.
This patch tries to make the handling consistent and return a helpful
error message in all cases.
This changes the parsing for "keyword" options so that if the option
is specified with no argument the argument is parsed as if it were
passed an empty string. This make it easier to add options to existing
boolean arguments (the existing --option can default to TRUE).
As we noticed when Jani kindly converted things to getopt_long, much
of the work in argument parsing in notmuch is due to the the key-value
style arguments like --format=(raw|json|text).
The framework here provides positional arguments, simple switches,
and --key=value style arguments that can take a value being an integer,
a string, or one of a set of keywords.
