Statsd-tags

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- Clean up tests and requirements.
- Encode socket data in ASCII.
- Tag v1.

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- Stop supporting IPv6. StatsD doesn't support it, and it breaks things.
- incr, decr, and gauge now support floating point values.

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- Add support for gauges.
- Add real docs and hook up ReadTheDocs.
- Add support for environment var configuration.

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- Look up IP addresses once per client instance.
- Support IPv6.

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- Improve StatsClient.timer.
- Remove nasty threadlocal stuff.
- Return result of StatsClient.timer.

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- Optional prefix for all stats.
- Introduce StatsClient.timer context decorator.