`OPT__ABBREV(&int_var)`::
Add `\--abbrev[=<n>]`.
+`OPT__COLOR(&int_var, description)`::
+ Add `\--color[=<when>]` and `--no-color`.
+
`OPT__DRY_RUN(&int_var)`::
Add `-n, \--dry-run`.
arguments. Short options that happen to be digits take
precedence over it.
+`OPT_COLOR_FLAG(short, long, &int_var, description)`::
+ Introduce an option that takes an optional argument that can
+ have one of three values: "always", "never", or "auto". If the
+ argument is not given, it defaults to "always". The `--no-` form
+ works like `--long=never`; it cannot take an argument. If
+ "always", set `int_var` to 1; if "never", set `int_var` to 0; if
+ "auto", set `int_var` to 1 if stdout is a tty or a pager,
+ 0 otherwise.
+
The last element of the array must be `OPT_END()`.