code: func (t *Table) SetSelectionChangedFunc(handler func(row, column int)) *Table {
  	t.selectionChanged = handler
  	return t
  }
docs: // SetSelectionChangedFunc sets a handler which is called whenever the user
  // navigates to a new selection. The handler receives the position of the new
  // selection. If entire rows are selected, the column index is undefined.
  // Likewise for entire columns.