code: func SaveBitmap(bitmap C.MMBitmapRef, gpath string, args ...int) string {
  	var mtype C.uint16_t = 1
  	if len(args) > 0 {
  		mtype = C.uint16_t(args[0])
  	}
  
  	path := C.CString(gpath)
  	saveBit := C.bitmap_save(bitmap, path, mtype)
  	C.free(unsafe.Pointer(path))
  
  	return C.GoString(saveBit)
  }
docs: // SaveBitmap save the bitmap to image
  //
  // robotgo.SaveBimap(bitmap C.MMBitmapRef, path string, type int)