* Boolean long options can be 'negated' (or 'unset') by prepending
`no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely,
options that begin with `no-` can be 'negated' by removing it.
+ Other long options can be unset (e.g., set string to NULL, set
+ integer to 0) by prepending `no-`.
* Options and non-option arguments can clearly be separated using the `--`
option, e.g. `-a -b --option -- --this-is-a-file` indicates that
Introduce an option with date argument, see `approxidate()`.
The timestamp is put into `int_var`.
+`OPT_EXPIRY_DATE(short, long, &int_var, description)`::
+ Introduce an option with expiry date argument, see `parse_expiry_date()`.
+ The timestamp is put into `int_var`.
+
`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
Introduce an option with argument.
The argument will be fed into the function given by `func_ptr`