code: func (document *Document) SaveAs(path string, format string, filter string) error {
  	cPath := C.CString(path)
  	defer C.free(unsafe.Pointer(cPath))
  	cFormat := C.CString(format)
  	defer C.free(unsafe.Pointer(cFormat))
  	cFilter := C.CString(filter)
  	defer C.free(unsafe.Pointer(cFilter))
  	status := C.document_save(document.handle, cPath, cFormat, cFilter)
  	if status != 1 {
  		return fmt.Errorf("Failed to save document")
  	}
  	return nil
  }
docs: // SaveAs saves document at desired path in desired format with applied filter rules
  // Actual (from libreoffice) error message can be read with Office.GetError