Talisker

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* Add a public testing helper (testing.talisker.TestContext), to isolate and collect talisker data in tests (329)
* Expose new talisker.testing.clear_all() api to make it easier to reset talisker state in (328)
* Add a timeout for prometheus locks, and asupport non-blocking locking in gevent (358)
* Do not enable prometheus multiprocess mode if there is only one gunicorn worker (358)
* Remove username/email from any user data in sentry (342)
* Add a relative-to-request start timestamp to all sentry breadcrumbs. (340)
* Support prometheus 0.4+ (334)

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* Improve the ip->name mapping for requests metric names (304)
* improve sentry report metadata, add tags and also sql statement summary (306)
* Track per-request sql/http/log costs (325)
* add explicit context clears at various points (305)
* TERM=dumb turns off terminal colors

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* Support statsd 3.3 (290)
* Properly serialize the prometheus worker cleanup (296)
* Gracefully fail if lock can't be initialised (303)

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A collection of minor improvements and fixes, and relicensing to Apache 2.

* Relicense to Apache-2 (258, 275) (thanks to Adam Collard)
* Aggregate prometheus metrics into one file on worker death. (281, 288)
* Wrapping logging and metrics code with try/except, so that we never fail (276)
* Fail more gracefully in the case where talisker has not been setup properly (264)
* Add support for TALISKER_REVISION_ID variable (262) (thanks to Robin Winslow and Adam Collard)
* Return sentry id from capture (261)
* Set level=warning in soft req. timeout sentry messages (255) (thanks to Guillermo Gonzalez)

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* Fix X-Request-Id to be a native string on py2 (247)

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* only set prometheus envvar in gunicorn runner, not for all runners (242)