ClockFace_menu: use addItems for settings

modules/ClockFace.md

@@ -174,4 +174,29 @@ Bangle.on('step', function(steps) {
   if (clock.paused === false) // draw step count
 });
 
+```
+
+
+ClockFace_menu
+==============
+If your clock comes with a settings menu, you can use this library to easily add
+some common options:
+
+```js
+
+let settings = require("Storage").readJSON("<appid>.settings.json", true)||{};
+function save(key, value) {
+  settings[key] = value;
+  require("Storage").writeJSON("<appid>.settings.json", settings);
+}
+
+let menu = {
+  "": {"title": /*LANG*/"<clock name> Settings"},
+};
+require("ClockFace_menu").addItems(menu, save, { 
+  showDate: settings.showDate, 
+  loadWidgets: settings.loadWidgets,
+});
+E.showMenu(menu);
+
 ```

modules/ClockFace_menu.js

@@ -1,4 +1,31 @@
-// boolean options, which default to true
+/**
+ * Add setting items to a menu
+ *
+ * @param {object} menu Menu to add items to
+ * @param {function} callback Callback when value changes
+ * @param {object} items Menu items to add, with their current value
+ */
+exports.addItems = function(menu, callback, items) {
+  Object.keys(items).forEach(key => {
+    let value = items[key];
+    const label = {
+      showDate:/*LANG*/"Show date",
+      loadWidgets:/*LANG*/"Load widgets",
+    }[key];
+    switch(key) {
+      case "showDate":
+      case "loadWidgets":
+        // boolean options, which default to true
+        if (value===undefined) value = true;
+        menu[label] = {
+          value: !!value,
+          onchange: v => callback(key, v),
+        };
+    }
+  });
+};
+
+// legacy boolean options
 exports.showDate =
 exports.loadWidgets =
   function(value, callback) {