Update keyed_helper to accept an 'attr' argument
Update keyed_helper to accept an 'attr' argument

Fixes #166  Ref #157

'attr' is shorthand for key=lambda o: getattr(o, attr), allowing
simpler syntax like helpers.link_to_model(attr='relatedobject')

doganmeh/django-datatable-view,pivotal-energy-solutions/django-datatable-view,pivotal-energy-solutions/django-datatable-view,doganmeh/django-datatable-view,pivotal-energy-solutions/django-datatable-view,doganmeh/django-datatable-view