Add support for selecting nested JSON objects

[chipkillmar]

Thanks for the great library!

We are using Cassandra Sink along with UDTs, and it would be great if KCQL supported selecting nested JSON objects.

For example:

create table person (
  id int,
  first_name text,
  last_name text,
  address frozen<address>,
  primary key (id)
);

create type address (
  street text,
  city text,
  state text,
  zip_code int
);

For the above data model, the following Cassandra insert statement works:

insert into person json '{"id":42,"first_name":"Bruce","last_name":"Wayne","address":{"street":"1007 Mountain Drive","city":"Gotham","state":"NY","zip_code":10012}}';

But this KCQL query fails with an IllegalArgumentException: Invalid path address when consuming Person records from Kafka:

select id, first_name, last_name, address from person.topic;