New features added

- Added compatibiliity for loader (require)
- Added clusterClassSelected option to set the cluster style when it is selected
- Added logic to keep a track of the selected cluster (it stills needs some "help" from the clusterer owner to be 100% effective)
- Added clusterSizeToZoom property so the cluster click can choose to zoomIn if the markers are greater than clusterSizeToZoom (even if zoomOnClick is disabled), ex: clusterSizeToZoom: 20, if you have zoomOnClick disabled and the cluster has 25 markers it will zoomIn anyways, the use case of this is that if you have markers < clusterSizeToZoom some info about the cluster is shown, but if the cluster has more markers it will zoomIn.
- Changed the behavior of the cluster click, now it just zoomsIn by 1 level (doesn't centers the map)