Redset

- Use `redis.Redis.pipeline` for doing atomic set operations, batching multiple
pops.

- Add builtin serializer `NamedtupleSerializer`
- Improve lock re: redis' spotty timestamp precision
- Increase test coverage
- Add coveralls to travis-CI

- Documentation updates

- Use `setuptools` now that distribute has been merged back into it

- Change serializer interface to match `json` (dump, load `->` dumps, loads)

- Spiked documentation with sphinx.
- Converted docstrings to ReST.