HPCC-0000 WIP - use iterators

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-0000 Use iterators, fix leaks

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-0000 Nested datasets

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-0000 Dictionaries, better error messages

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>