close levigo.Read/WriteOptions
add Flush to diff cache
move command handling to cmd package
don't set cache to nil after flushing
pool idRefs/bytes in diff cache
do not leak Ticker in closed stats reporter
read geojson with z-values
do not auto destroy BoundsPolygon
make db schema configurable from cmd-line and config.json
return errors from newTxRouter
automatically transform GeoJSON in WGS84 to webmercator
remove duplicate geojson reader code