Added null checking to controller and action to prevent null reference exceptions from being thrown when route values are set to null. Fixed some spelling mistakes in the comments of SiteMapNode.cs
Updated MVC 4 and dependency version references to be consistent throughout the solution to 4.0.20710.0.
Updated SimpleInjector module to exclude SiteMapNodeCreator and DynamicSiteMapNodeBuilder from the configuration so the SimpleInjector.Verify method will work.
Fixes #253, culture formatting affecting string formatting of priority element in sitemap.xml endpoint.