Added SOXT_WIDGET_CALLBACK macro for prototyping Xt callbacks, and SOXT_WIDGET_CALLBACK_IMPLEMENTATION for generating the standard parts of the callback implementations.
Added SOXT_WIDGET_CALLBACK macro for prototyping Xt callbacks, and
SOXT_WIDGET_CALLBACK_IMPLEMENTATION for generating the standard parts
of the callback implementations.

Alexpux/SoXt,Alexpux/SoXt,Alexpux/SoXt,Alexpux/SoXt