Add initial Date bindings

Doesn't do much, yet, because we can't get the timezone with a plain binding, but it's at least something.

tests/compiler.js

@@ -192,7 +192,8 @@ tests.forEach(filename => {
             math: {
               mod: function(a, b) { return a % b; }
             },
-            Math: Math,
+            Math,
+            Date,
 
             // tests/declare
             declare: {