code: func (v *TextBuffer) GetMark(mark_name string) *TextMark {
  	cstr := C.CString(mark_name)
  	defer C.free(unsafe.Pointer(cstr))
  	ret := C.gtk_text_buffer_get_mark(v.native(), (*C.gchar)(cstr))
  	return (*TextMark)(ret)
  }
docs: // GetMark() is a wrapper around gtk_text_buffer_get_mark().