Add wear de4tect library based on http://forum.espruino.com/conversations/379538/ and https://github.com/espruino/Espruino/pull/2264

modules/wear_detect.js

@@ -0,0 +1,20 @@
+/** Returns a promise that resolves with whether the Bangle
+is worn or not.
+
+Usage:
+
+require("wear_detect").isWorn().then(worn => {
+  console.log(worn ? "is worn" : "not worn");
+});
+*/
+exports.isWorn = function() {
+  return new Promise(resolve => {
+    if (Bangle.isCharging())
+        return resolve(false);
+    if (E.getTemperature() > 24.625)
+        return resolve(true);
+    if (Bangle.getAccel().mag > 1.045)
+        return resolve(true);
+    return resolve(false);
+  });
+};