Introduce an option with integer argument.
The integer is put into `int_var`.
+`OPT_MAGNITUDE(short, long, &unsigned_long_var, description)`::
+ Introduce an option with a size argument. The argument must be a
+ non-negative integer and may include a suffix of 'k', 'm' or 'g' to
+ scale the provided value by 1024, 1024^2 or 1024^3 respectively.
+ The scaled value is put into `unsigned_long_var`.
+
`OPT_DATE(short, long, &int_var, description)`::
Introduce an option with date argument, see `approxidate()`.
The timestamp is put into `int_var`.