Jsdoc index filtering support

I've confirmed this works on Chrome, Firefox & IE8, but have yet to test IE9, IE10 & IE11. Also, it's worth noting that IE8 and IE9 won't have combo-box support, but will still be able to enter package filters. If this works in those browsers than we should create a pull-request for the 'index-filtering' branch in the our 'jsdoc3' fork.