code: func (f *Fpdf) SetFooterFunc(fnc func()) {
  	f.footerFnc = fnc
  	f.footerFncLpi = nil
  }
docs: // SetFooterFunc sets the function that lets the application render the page
  // footer. The specified function is automatically called by AddPage() and
  // Close() and should not be called directly by the application. The
  // implementation in Fpdf is empty, so you have to provide an appropriate
  // function if you want page footers. fnc will typically be a closure that has
  // access to the Fpdf instance and other document generation variables. See
  // SetFooterFuncLpi for a similar function that passes a last page indicator.
  //
  // This method is demonstrated in the example for AddPage().