implement UnregisterMultiple

[stefanmoser]

This is an implementation of UnregisterMultiple. The main reason this is needed is that RegisterMultiple uses a convention to register each type as a named type with the full name of the type. Therefore if you had previous registered a type using...

container.RegisterMultiple<TInterface>(new [] { type });

...you would then have to unregister the type using...

container.Unregister<TInterface>(type.FullName);

This is a little unintuitive. This PR allows you to unregister the type using...

container.UnregisterMultiple<TInterface>(new [] { type });

...which is the same syntax that the type was originally registered.

[stefanmoser]

I was unsure about including the commented out #if NETFX_CORE. This code was copied from the implementation of public MultiRegisterOptions RegisterMultiple(Type registrationType, IEnumerable<Type> implementationTypes) so I left it in for consistency.

[niemyjski]

Could you please resolve the merge conflicts and well get this merged.