Restlib2

**Bugs**
- 9 - Decodes the body as UTF-8 before deserializing into the specified Content-Type

The setup.py file has been updated to ensure the six package is at least version 1.4.0.

Fix is a small release that removes the need to explicitly pass content in `Resource.render`. In addition all responses will be checked for whether they do not contain content and will have their status code set to `204 No Content` if the following conditions are met:
- The status code is `200 OK`
- The content is empty
- The response does not contain a `Content-Disposition` header

See 7 for details

**Features**
- Python 3 support

**Enhancements**
- Param cleaning error messages are now propagated in raised exceptions or log calls

**Changes**
- Remove deprecated `param_cleaners`

Inherited parameter fields were being overwritten.