FileSystemTileCache: check for NPE in deleteDirectory
Docs: added README.md
Writer: fix to area detection heuristic issue #526
Writer: fix to c9e724f98950eb, fixes issue #526
MapViewerTemplate: added fix for when map file has start position, but no start zoom level
Samples/RenderthemeV4: added another base layer to display topographic info (cat natural in rendertheme-v4.xml)
Docs: added changes suggested by mvglasow, fixes #507