INT-2853 ObjectToStringTransformer Improvements

* Convert byte[] and char[] to String rather than simply using toString().
* Allow the charset to be configured for byte[] payloads.
* Add tests.
* Add reference documentation updates.
Merge pull request #734 from garyrussell/INT-2853

* garyrussell-INT-2853:
  INT-2853 ObjectToStringTransformer Improvements