removed old memory mapped binning store
renamed SimpleSpatialBinSore to MemoryBackedSpatialBinStore
created FileBackedSpatialBinStore
created SortedSpatialBinList
changed interface SpatialBinStore
created GeneralSpatialBinStore
using new BinStore
added BinWriterTest
renamed SpatialBinStore to SpatialBinCollector and its implementations correspondingly