Sprockets.mixins.metrics

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- Add configuration documentation
- Exclude Tornado >6 (as-yet-unreleased version)
- Add :func:`sprockets.mixins.metrics.statsd.get_client` function
- Add :meth:`sprockets.mixins.metrics.statsd.StatsDCollector.close` method

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- Add support for Tornado 5
- Remove support for Tornado < 5
- Remove support for Python < 3.7
- Remove InfluxDB support (use `sprockets-influxdb`_)

.. _sprockets-influxdb: https://github.com/sprockets/sprockets-influxdb

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- Fixed bad formatted TCP StatsD messages by appending a newline

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- Add TCP support to StatsD

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- Loosen Tornado pin to include 4.4.

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- Fix retrival of status code.