Introduce a boolean option.
If used, `int_var` is bitwise-ored with `mask`.
+`OPT_NEGBIT(short, long, &int_var, description, mask)`::
+ Introduce a boolean option.
+ If used, `int_var` is bitwise-anded with the inverted `mask`.
+
`OPT_SET_INT(short, long, &int_var, description, integer)`::
Introduce a boolean option.
If used, set `int_var` to `integer`.
`OPT_ARGUMENT(long, description)`::
Introduce a long-option argument that will be kept in `argv[]`.
+`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
+ Recognize numerical options like -123 and feed the integer as
+ if it was an argument to the function given by `func_ptr`.
+ The result will be put into `var`. There can be only one such
+ option definition. It cannot be negated and it takes no
+ arguments. Short options that happen to be digits take
+ precedence over it.
+
The last element of the array must be `OPT_END()`.