add chunkCount to 0x38

changed some more things for more API consistency

 * 0x33: compressedData -> compressedChunkData
 * 0x38: meta.chunkX -> meta.x
 * 0x38: meta.chunkZ -> meta.z
 * 0x38: meta.primaryBitMap -> meta.bitMap
 * 0x38: add chunkCount
Release 0.4.0