task/us93-ta70 -- SQL to extract details from the RETURNS table based
on id - functional

nparcel/dbsession.py
* new attribute db_type that captures the database type (for example,
  ``sqlite`` or ``MSSQL``)

nparcel/table/__init__.py
* update the __init__() signature to accept an alias parameter

nparcel/table/returns_reference.py
* new method reference_nbr_sql() to provide an SQL wrapper to extract
  the returns_reference.reference_nbr of items relating to returns_id

nparcel/table/returns.py
* new method extract_id_sql() SQL wrapper to extract the returns
  against id

nparcel/dbsession.py
* port sqlite library to sqlite3