Allow implicit context iteration with each

Fixes #671

lib/handlebars/base.js

@@ -80,6 +80,12 @@ function registerDefaultHelpers(instance) {
   });
 
   instance.registerHelper('each', function(context, options) {
+    // Allow for {{#each}}
+    if (!options) {
+      options = context;
+      context = this;
+    }
+
     var fn = options.fn, inverse = options.inverse;
     var i = 0, ret = "", data;