prepared for unit tests
GridClusteringStrategy tests
GridClusteringStrategy test
GoogleMap.getDisplayedMarkers
all markers returned from getDisplayedMarkers when using addMarkersDynamically
GoogleMap.getMinZoomLevelNotClustered stub
typo
GoogleMap.getMinZoomLevelNotClustered tests
GridClusteringStrategy.getMinZoomLevelNotClustered implementation
fixed infinite loop when two markers have the same position
updated javadoc