code: func (v *TextBuffer) CreateMark(mark_name string, where *TextIter, left_gravity bool) *TextMark {
  	cstr := C.CString(mark_name)
  	defer C.free(unsafe.Pointer(cstr))
  	ret := C.gtk_text_buffer_create_mark(v.native(), (*C.gchar)(cstr), (*C.GtkTextIter)(where), gbool(left_gravity))
  	return (*TextMark)(ret)
  }
docs: // CreateMark() is a wrapper around gtk_text_buffer_create_mark().