Create typeof.js

Add implementation of javascript "typeof".
Implementation is based on json.js call which will yield a inline string as a result.

Registration into helpers list is required if approved.
https://github.com/bigcommerce/paper-handlebars/blob/master/helpers.js

helpers/typeof.js

@@ -0,0 +1,14 @@
+'use strict';
+const common = require('./lib/common.js');
+
+const factory = globals => {
+    return function(data) {
+        data = common.unwrapIfSafeString(globals.handlebars, data);
+        return typeof data;
+    };
+};
+
+module.exports = [{
+    name: 'typeof',
+    factory: factory,
+}];