pinChangeInterrupts.ino

const int button = PORTD5;
const int led = PORTD2;

void setup() {
  // put your setup code here, to run once:
  DDRD = _BV(led); //Configure LED for output, button is input
  PORTD = _BV(button); //Enable button on button pin

  PCICR = _BV(PCIE0); //Enable Pin Change Interrupt 0
  PCMSK0 = _BV(PCINT5); //Mask out all other bits besides pin 5 (button)
}

void loop() {
}

ISR(PCINT0_vect){ //When button changes state,
  PORTD ^= _BV(led); //Toggle LED 
}