Autofac.WebApi2 4.0.0

Fixed #6 and #14: The Autofac filter interfaces now use Task/async based method signatures rather than synchronous signatures. This avoids using Task.Run or other methods to convert async to synchronous where HttpContext.Current could sometimes get lost. Fixed #8: Marked RegisterModelBinders as obsolete since it doesn't actually register the model binders such that they hook into dependency injection. Use the AsModelBinderForTypes() extension on binder registrations instead. Fixed #10: Controller types that derive from base controllers can add action filters to non-virtual methods. Switched to .NET 4.5 security model (no more AllowPartiallyTrustedCallersAttribute).