Opentracing-instrumentation

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- Support non TornadoScopeManager in traced_function decorator (86) <Vasilii Novikov>
- Add support for Celery (85) <Aliaksei Urbanski>
- Add tags.HTTP_METHOD to before_request (79) <Nicholas Amorim>
- Using opentracing.ext in all hooks. (78) <Nicholas Amorim>
- Add support for boto3 (77) <Aliaksei Urbanski>
- Support Composable object as sql statement for psycopg2 (82) <Vasilii Novikov>
- Add support for Tornado 5 (76) <Vasilii Novikov>
- Fix compatibility with Peewee ORM (72) <Aliaksei Urbanski>

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- Unpin OpenTracing upper bound to <3

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- Upgrade to OpenTracing 2.0 API (54) <Carlos Alberto Cortez>
- Permit the injection of specific parent span (73) <CARRIERE Etienne>
- Fix `opentracing_instrumentation.client_hooks.strict_redis.reset_patches` method
- Add `response_handler_hook` to `requests` instrumentation (66) <Aliaksei Urbanski>
- Add unit test for ThreadSafeStackContext (71) <Yuri Shkuro>
- Improve testing (70) (5 months ago) <Aliaksei Urbanski>
- Add tox.ini
- Update setup.cfg
- Enable branch coverage measurement
- Update the README
- Unify tracer fixture and move it to conftest.py
- Fix some deprecation warnings
- Clean up imports
- Update supported Python versions (+3.7, -3.3) (69) <Aliaksei Urbanski>
- Fix function call in code example (67) <Charlotte Iwasaki>

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- Fix Makefile to check Python version to determine setuptools version (62)
- Fix gettattr for ContextManagerConnectionWrapper (63)

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- Fix wrapper for psycopg2 connection so type check does not fail (55)

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- Remove dependency on 'futures' (47)