Enhancements to IoBufferHexDumper

[Jonathan Valliere]

I'm adding some additional methods to IoBufferHexDumper to produce pretty
hex dumps for debugging purposes.

Possible options to expose the new methods:

   1. Making IoBufferHexDumper class public instead of package local
   2. Add another public method to IoBuffer (e.g.
   IoBuffer#getPrettyHexDump() or #getVerboseHexDump()
   3. Overload IoBuffer#getHexDump() to include "boolean pretty" to enable
   pretty dumps.

Anyone have any opinions?