Fastest IO toggle

... just had a play at adding that peek/poke fast path. Try this now:

function foo() {
  "compiled";
  var GPIOB = 0x40020418; // BSRR register
  var PIN = 1 << 2;
  var cnt = 10000000;
  var t = getTime();
  for (var i=0;i<cnt;i++) {
    poke32(GPIOB, PIN); // on 
    poke32(GPIOB, PIN<<16); // off
  }
  console.log((cnt / (1000000*(getTime()-t))) + " Mhz");
}

LED1.set(); // set up as output first
foo();

And for me it reports 7.7Mhz, which is just a bit faster :)