Ddtrace

**Bug fixes**

* [core] remove the root logger configuration within the library (556)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.13.0...v0.13.1) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/24?closed=1).
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**New integrations**
- [`pymemcache`](https://github.com/pinterest/pymemcache) integration (#511)

**Celery integration**

Due to some limitations with our Celery integration, we changed our instrumentation to a [signals based approach](http://docs.celeryproject.org/en/latest/userguide/signals.html). We also started using import hooks to instrument Celery, so that enabling the instrumentation doesn't trigger a `celery` import.

- Signals implementation: 530
- Moving to import hooks: 534
- Resolved issues: 357, 493, 495, 495, 510, 370

**Breaking changes**
Using the signal based approach increase the stability of our instrumentation, but it limits what is currently traced. This is a list of changes that are considered breaking changes in the behavior and not in the API, so no changes are needed in your code unless you want a different behavior:
- By default all tasks will be traced if they use the Celery signals API, so tasks invoked with methods like `apply()`, `apply_async()` and `delay()` will be traced but tasks invoked with `run()` will **not** be traced.
- `patch_task()` is deprecated; if it's used, all tasks will be instrumented

**Bug fixes**
- [core] check if bootstrap dir is in path before removal (516 -- thanks beezz!)
- [core] have hostname default to `DATADOG_TRACE_AGENT_HOSTNAME` environment variable if available (509, 524 -- thanks hfern!)
- [core] add WSGI-style http headers support to HTTP propagator (456, 522)
- [core] Enable buffering on `getresponse` (464, 527)
- [core] configure the root logger (536)
- [aiopg] set the `app_type` during initialization (492, 507)
- [boto] default to `None` if no region (525, 526)
- [flask] avoid double instrumentation when `TraceMiddleware` is used (538)
- [pymongo] fix multiple host kwargs (535)
- [tornado] make settings object accessible during configuration (499, 498 -- thanks kave!)

**Improvements**
- [core/helpers] add a shortcut to retrieve Trace correlation identifiers (488)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.12.1...v0.13.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/21?closed=1).
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**Bugfixes**

* [celery] add support for celery v1 tasks (old-style tasks) (465, 423)
* [celery] `ddtrace-run` broke third-party script support; now it handles correctly the `argv` params (469, 423)
* [celery] patch `TaskRegistry` to support old-style task with `ddtrace-run` (484)
* [django] update error handling if another middleware has handled the exception already (418, 462)
* [django] `DatabaseWrapper` loaded in right thread, after removing `setting_changed` signal from the `DatadogSettings` (481, 435)
* [django/celery] add `shared_task` decorator wrapper to trace properly Celery tasks (486, 451)
* [django/docs] notes about Debug Mode, and debugging (476 -- thanks ndkv!)
* [gevent] pass `sampling_priority` field when Distributed Tracing is enabled (457)
* [mysqlb] add missing services info when they're flushed (468, 428)
* [psycopg2] properly patch the driver when `quote_ident` typing is used (477, 474, 383)
* [pylons] ensure the middleware code is Python 3 compatible to avoid crashes on import (475, 472)
* [requests] add missing services info when they're flushed (471, 428)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.12.0...v0.12.1) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/19?closed=1).
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**New integrations**
* [boto] Botocore and boto instrumentation is enabled by default using `patch_all()` (319)
* [futures] provide context propagation for `concurrent` module (429, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.futures))
* [mysql] add `pymysql` support (296, [docs](http://pypi.datadoghq.com/trace/docs/#mysql) -- thanks wklken)

**Improvements**
* [core] introducing a low-level API to define configurations for each integration. This API is used only by the `requests` module and will be implemented in other integrations in newer releases (445, 443, 450, 454, 441)
* [celery] split the service name in `celery-producer` and `celery-worker` for better stats (432)
* [falcon] add distributed tracing (437)
* [requests] provide a default service name for the request `Span` (433)
* [requests] add `split_by_domain ` config to split service name by domain (434)
* [tornado] better compatibility using `futures` instrumentation (431)

**Bugfixes**
* [core] ensure `sitecustomize.py` is imported when `ddtrace-run` wrapper is used (458)
* [flask] use `ddtrace` logger instead of Flask to avoid having a custom log filter (447, 455)

**Breaking changes**
* [celery] the name of the service is now split in two different services: `celery-producer` and `celery-worker`. After the upgrade, you'll stop sending data to what was the default service name (`celery`). You should check the new services instead because you'll see a drop. Previously reported traces in the `celery` service, are still available if you move back the time selector.

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.11.1...v0.12.0) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/17?closed=1).
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**Improvements**

* [bottle] use the `route` argument in `TracePlugin`, to support Bottle 0.11.x (439)

**Bugfixes**

* [django] gunicorn gevent worker wasn't instrumenting database connections (442)
* [django] remove `MIDDLEWARE_CLASSES` deprecation warning from tests (444)
* [django] ensure only `MIDDLEWARE` or `MIDDLEWARE_CLASSES` are loaded with tracing middlewares (446)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.11.0...v0.11.1) and the [release milestone](https://github.com/DataDog/dd-trace-py/milestone/18?closed=1).
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**Security fixes**

* [dbapi] remove `sql.query` tag from SQL spans, so that the content is properly obfuscated in the Agent. This security fix is required to prevent wrong data collection of reported SQL queries. This issue impacts only MySQL integrations and NOT `psycopg2` or `sqlalchemy` while using the PostgreSQL driver. (421)

**New integrations**

* [django] add support for Django 2.0 (415 -- thanks sciyoshi!)
* [mysql] `MySQL-python` and `mysqlclient` packages are currently supported (376 -- thanks yoichi!)
* [psycopg2] add support for version 2.4 (424)
* [pylons] Pylons >= 0.9.6 is officially supported (416)

**Bugfixes**

* [core] `ddtrace-run` script accepts `DATADOG_PRIORITY_SAMPLING` to enable [Priority Sampling](http://pypi.datadoghq.com/trace/docs/#priority-sampling) (426)
* [pylons] add distributed tracing via kwarg and environment variable (425, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.pylons))
* [pylons] `ddtrace-run` script can patch a `PylonsApp` (416)
* [pylons] add tracing to Pylons `render` function (420)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.10.1...v0.11.0) and [0.11.0 milestone](https://github.com/DataDog/dd-trace-py/milestone/15?closed=1).
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