Ddtrace

This is a bug fix release that requires no changes.

This release includes a fix for context propagation with `futures`. Under the right conditions we could incorrectly share a trace context between multiple `futures` threads which result in multiple traces being joined together in one.

Changes
Bug fixes
* [core] Allow futures to skip creating new context if one doesn't exist (806)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.20.2...v0.20.3) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/37?closed=1).
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No changes are needed to upgrade to `0.20.2`.

This big fix release includes changes to ensure we properly read the HTTP response body from the trace agent before we close the HTTP connection.

Changes
Bug fixes

- [core] Call HTTPResponse.read() before HTTPConnection.close() (800)

Improvements
- [tests] limit grpcio version to >=1.8.0,<1.18.0 (802)
- [tools] Add confirmation to 'rake pypi:release' task (791 )

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.20.1...v0.20.2) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/36?closed=1).
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No changes are needed to upgrade

Changes
Bug fixes
[celery] Ensure `celery.run` span is closed when task is retried (787)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.20.0...v0.20.1) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/36?closed=1).
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We have added support for logs injection to the tracer. If you are already using `ddtrace-run`, the integration can be enabled with setting the environment variable `DD_LOGS_INJECTION=true`. The default behavior once logs injection is enabled is to have trace information inserted into all log entries. If you prefer more customization, you can manually instrument and configure a log formatter with the tracer information.

Changes

New Integrations

* [mako] Add Mako integration (779 -- thanks wklken)

Enhancements

* [core] Tracer and logs integration (777)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.19.0...v0.20.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/34?closed=1).
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With `0.19.0` we have decided to disable the tracing of `dbapi2` `fetchone()`/`fetchmany()`/`fetchall()` methods by default.

This change effects all integrations which rely on the `dbapi2` API, including `psycopg2`, `mysql`, `mysqldb`, `pymysql`, and `sqlite3`.

We have introduced this change to reduce the noise added to traces from having these methods (mostly `fetchone()`) traced by default.

With `fetchone()` enabled the traces received can get very large for large result sets, the resulting traces either become difficult to read or become too large causing issues when flushing to the trace agent, potentially causing traces to be dropped.

To re-enable the tracing of these methods you can either configure via the environment variable `DD_DBAPI2_TRACE_FETCH_METHODS=true` or manually via:

python
from ddtrace import config
config.dbapi2.trace_fetch_methods = True


Changes
Bugs
[dbapi2] disable fetchone/fetchmany/fetchall tracing by default (780)
[opentracing] Fixing context provider imports for scope manager (771 -- thanks Maximilien-R)

Enhancements
[tests] test python setup.py sdist and twine check on build (782)
[core] Add API to configure Trace Search (781)
[core] Enable priority sampling by default (774)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.18.0...v0.19.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/32?closed=1).
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New Integrations

* [molten] Add molten support (685)

Bug Fixes

* [aws] Blacklist arguments stored as tags (761)
* [psycopg2] Fix composable query tracing (736)

Improvements

* [aiohttp] Add HTTP method to the root span resource (652 -- thanks k4nar)
* [aws]Flatten span tag names (768)
* [opentracer] Set global tags (764)
* [core] add six and replace custom compat functions (751)
* [config] make IntegrationConfig an AttrDict (742)
* [tests] remove unused monkey.py test file (760)
* [tests] fix linting in test files (752)
* [psycopg2] fix linting issues (749)
* [tests] have most tests use pytest test runner (748)
* [tests] Provide default implementation of patch test methods (747)
* [tests] run flake8 on all test files (745)
* [tests] Add patch mixin and base test case (721)
* [tests] Add Subprocess TestCase (720)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.17.1...v0.18.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/30?closed=1).
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