Implement option to show selected <optgroup>'s label
Reapplied css for group name
moved choice_label to AbstractChosen
Added documentation
Merge remote-tracking branch 'koenpunt/include-group-labels' into features/show-opt-group-in-display
Including code from koenpunt which allows display of opt group

https://github.com/harvesthq/chosen/pull/1610

if this ever gets merged we could dump this fork, but i've added it to c5 so we own it