Implement lookup helper

lib/handlebars/base.js

@@ -193,6 +193,10 @@ function registerDefaultHelpers(instance) {
     var level = options.data && options.data.level != null ? parseInt(options.data.level, 10) : 1;
     instance.log(level, context);
   });
+
+  instance.registerHelper('lookup', function(obj, field, options) {
+    return obj && obj[field];
+  });
 }
 
 export var logger = {

lib/handlebars/compiler/compiler.js

@@ -85,7 +85,8 @@ Compiler.prototype = {
       'if': true,
       'unless': true,
       'with': true,
-      'log': true
+      'log': true,
+      'lookup': true
     };
     if (knownHelpers) {
       for (var name in knownHelpers) {