Make sidebars using Bootstrap's affix play nicely with responsive designs

fluidAffix.js

    $.fn.fluidAffix = function(opts){

        return this.each(function(){

            var $this = $(this);
            var $parent = $this.parent();

            // Match width of parent container
            $this.css('width', $parent.width()+'px');

            // Adjust top offset dynamically
            var _top = $this.offset().top;
            
            // If a container selector is supplied, add the offset difference for
            // a cleaner transition
            if (opts.container){
                var _ctop = $(opts.container).offset().top;
                _top += _top - _ctop;
            }
            
            $this.affix({
                offset : {
                    top : _top
                }
            });

        });
    };