Added totalPin mapping for the MEGA

Mapped The totalPins for the mega. To be fair its a small commit and still doesn't fix issues with the MEGA but it's a step in the right direction.

Used this to map pins, it will make pin mapping easy in future for other boards:

	five.Board().on("ready", function() {

	  var pi = [];
	  var pins = this.firmata.pins;

	  for ( var i in pins ){

		pi.push( pins[i].supportedModes.length );
	  }
	  console.log( pi );

	});