added api header file for image proeccesing routines.  Initially just has Cmiss_field_create_binary_threshold_image_filter routine and a Cmiss_field_binary_threshold_image_filter_cast routine
added api header file for image proeccesing routines.  Initially just has Cmiss_field_create_binary_threshold_image_filter routine and a Cmiss_field_binary_threshold_image_filter_cast routine

cmiss/cmgui,cmiss/cmgui