Serialization keeps track of serialization types of variables so can
create containers holding them.
Keeping track of whether serialized and deserialized variables are tvars so can decide on how to serialize and deserialize them.
Moved deserialization into its own module (outside of context).  Additionally, deserialize differently depending on whether internal object is tvar or not.
Set is_tvars when not passing back args.
Added basic ralph src for struct serialization.
Added test harness to ensure that struct serialization works.  It
currently doesn't.