Added getChildCount and getAllChildMarkers
Added getChildCount and getAllChildMarkers

methods to Methods section (previously they were mentioned only in the Customising section).

Leaflet/Leaflet.markercluster,frenomus/Leaflet.markercluster,ghybs/Leaflet.markercluster,604557209/byzgf,ghybs/Leaflet.markercluster,nerik/Leaflet.markercluster,zverev/Leaflet.markercluster,Leaflet/Leaflet.markercluster,nerik/Leaflet.markercluster,zverev/Leaflet.markercluster,604557209/byzgf,frenomus/Leaflet.markercluster