Redis-collections

This is a bugfix release to incorporate the issues fixed by 57 and 63, which prevent setup from succeeding on some platforms.

Version 0.2.0 supports Python 3 and make several changes:

These PRs were part of the release:
- 43 - Fixes `Set` inheritance
- 44 - Added Initial Python 3 support
- 45 - Re-worked `Dict` classes to accept non-string keys
- 46 - Added local caching for using mutable values with `Dict` instances and the new `DefaultDict`
- 47 - Fixes for `List` slicing
- 52 - Added local caching for using mutable values with `List` instances

**Note**: There are some backward-incompatible changes with previous versions, particularly with `Dict`. `Dict` instances no longer have a `discard` method, and do not access Redis the same way as before (so do not attempt to use this version with a Redis collection created by a previous version).

Incorporates the fix for the issue reported in PR 29 and 32.