better ToString() support for enums and container types

The Delphi library has limited support for ToString(), i.e. printing structured Thrift data into some textual form. Where it currently falls short is two places:

a) enum types are always rendered in their numeric representation

b) list<>,  map<> and set<> are shown only in their most generic form (i.e. the underlying classname of the container) which is less useful either.