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`