Treat numbers as numbers in expressions

This is so that `{{ 1 }} ` is treated as `1` and not as `model.1`.
Same goes for `{{ 1.2 }}` which should not be treated as `model.1.2`.

Fixes #24

src/polymer-expressions.js

@@ -592,6 +592,10 @@
       case 'true':
         return true;
     }
+
+    if (!isNaN(Number(name)))
+      return true;
+
     return false;
   };
 
@@ -638,20 +642,17 @@
         return prepareEventBinding(path, name, this);
       }
 
-      if (path.valid) {
+      if (!isLiteralExpression(pathString) && path.valid) {
         if (path.length == 1) {
-          if (!isLiteralExpression(path[0])) {
-            return function(model, node, oneTime) {
-              if (oneTime)
-                return path.getValueFrom(model);
-
-              var scope = findScope(model, path[0]);
-              return new PathObserver(scope, path);
-            };
-          }
-        } else {
-          return; // bail out early if pathString is simple path.
+          return function(model, node, oneTime) {
+            if (oneTime)
+              return path.getValueFrom(model);
+
+            var scope = findScope(model, path[0]);
+            return new PathObserver(scope, path);
+          };
         }
+        return; // bail out early if pathString is simple path.
       }
 
       return prepareBinding(pathString, name, node, this);