... and argument order in FL_INLINE_CALLBACK_2 macro
* adds FL/fl_callback.macros.H * adds FL_FUNCTION_CALLBACK_n(widget, function, [type, data]) * adds FL_METHOD_CALLBACK_n(widget, class, instance, method, [type, data]) * adds FL_INLINE_CALLBACK_n(widget, [type, name, data], callback_body) * adds `examples/callback` * full documentation