Merge pull request #9 from RobertSudwarts/develop

Resolved 'is not JSON serializable' error for datetime.date objects
Amendments made to the SQLAjqGridWidget.prepare()
'caption': if not set, uses __name__
'sortname': will use column specified in 'options'
            or defaults to `pkey`

  modified:   tw2/jqplugins/jqgrid/widgets/sqla.py