Refactor for uniformity of connection string option

All connections now expect the connection string defined as
`connection`, while `uri` will continue to function it is officially
deprecated in its use.
3.1 enhancesments and message handling refinement

- More message properties and attributes now supported
- Body/Message encoding is now configurable at runtime at construction
  - Supported Encodings:
    - base64
    - utf-8
  - This provides and future entry point for mesage encryption support
- routing_key now works
- added new message properties:
  - correlation_id
  - reply_to
removed JSON_ESCAPE_SLASHES to support `php-5.3`