Using Zero-Copy API to read

Replace all the byte array based API with Byte Buffer based API in the reading path to avoid byte array copy.
1.Introduce a Compatible layer to keep compatible with old Hadoop API
2.Make the whole read path use ByteBuffer directly

as ```in``` is wrapping a ByteBuffer we could directly pass the buffer to ```unpack8Values``` instead of reading to a byte array that we wrap into a ByteBuffer.