New joint DHT11/DHT22 module

@MaBe I've just committed some code specifically for DHT22 - please could you give it a test?

// DHT22
var dht = require("https://raw.githubusercontent.com/espruino/EspruinoDocs/master/devices/DHT22.js").connect(pin);
// or use "https://raw.githubusercontent.com/espruino/EspruinoDocs/master/devices/DHT11.js" for DHT11

setInterval(function() {
  dht.read(
    function(a){
      console.log("Temp is "+a.temp.toString()+
                  " and RH is "+a.rh.toString());
});}, 5000);