Add ability to use a function for maxClusterRadius
Add ability to use a function for maxClusterRadius

I find it's necessary to use a different radius at different zoom levels. This patch lets you continue to use a single number for all zoom levels, but also lets you use a function to vary the radius for each zoom level.
paulserraino/leaflet-geojson-cluster,zverev/Leaflet.markercluster,nerik/Leaflet.markercluster,VincentDS/Leaflet.markercluster,tobias-johansson/Leaflet.markercluster,alex2wong/Leaflet.markercluster,hoganmaps/Leaflet.markercluster,paulserraino/leaflet-geojson-cluster,mr47/Leaflet.markercluster,lrpauley/Leaflet.markercluster,lrpauley/Leaflet.markercluster,mr47/Leaflet.markercluster,tobias-johansson/Leaflet.markercluster,ghybs/Leaflet.markercluster,cyrilchaponeverysens/Leaflet.markercluster,604557209/byzgf,nerik/Leaflet.markercluster,zverev/Leaflet.markercluster,zoutepopcorn/Leaflet.markercluster,MazeMap/Leaflet.markercluster,Leaflet/Leaflet.markercluster,frenomus/Leaflet.markercluster,MazeMap/Leaflet.markercluster,frenomus/Leaflet.markercluster,VincentDS/Leaflet.markercluster,Leaflet/Leaflet.markercluster,Intermaps/Leaflet.markercluster,zoutepopcorn/Leaflet.markercluster,hoganmaps/Leaflet.markercluster,ghybs/Leaflet.markercluster,alex2wong/Leaflet.markercluster,Chuck8080/web-maps-markercluster,Intermaps/Leaflet.markercluster,radnor/Leaflet.markercluster,cyrilchaponeverysens/Leaflet.markercluster,radnor/Leaflet.markercluster,604557209/byzgf