Motivation:
The use of ByteBuffer for IO operations adds more flexibility as ByteBuffers
can be sliced, shared and passed directly to various channels. Moreover, any
byte array can be easily wrapped into ByteBuffer, if needed.

Modification:
added vfs#read and vfs#write methods with default implementation falling
back to byte array based methods to maintain backward compatibility. Updated
OperationREAD and OperationWRITE to use the new methods. Deprecate byte
array based methods.

Result:
more flexibility with same functionality.

Acked-by: Paul Millar
Target: master