Ignore lists of lists in JSON, reenable feature

The way that lists of lists are represented in the generated code is
as an opaque pointer list. The JSON code needs a typed representation
in order to walk and print the value.

Just ignore for now. Lists of lists aren't widely used because people
have to manage the types themselves.
Merge pull request #3 from glycerine/fixjson

Ignore lists of lists in JSON, reenable feature