- Require an instance of SerializationSettings for serializers and
   deserializers.

IStreamWriter to allow writers to directly create readers.

usres can't change the set of allowed types after it is set and handed
to the deserialization code.

Remove the ability for FastSerialization to create arbitrary types that
are specified in serialized files.  Instead, force users to register all
types before or during serialization.  Types can be registered via calls
to Deserializer.RegisterType and Deserializer.RegisterFactory.  Users
can also implement Deserializer.OnUnregisteredType to handle
unregistered types encountered during deserialization.  It is incumbent
on the implementor to not just blindly call Type.GetType in
OnUnregisteredType, and instead only create known types.

provide enough context to find the right assembly.