Clean up
Add `render` method for composing an HttpResponse from the handler

This provides a clean way to override/extend building an HttpResponse
in subclasses.
Add check for 'no content' responses
Add support for passing keyword args upon initialization

This enables creating and instance 'on-the-fly' without
needing to subclass for simple customization.
Add TemplateResponseMixin (and TemplateResource)

This provides an easy entry point for using restlib2 as an
alternative to Django's CBVs, but with the benefit of not being
tied down with conventional cruft.
0.3.1 Release
0.3.2 Bump