Ddtrace

**New features**

* [core] add process ID in root spans metadata (293)

**Improvements**

* [falcon] extended support for Falcon 1.2; improved error handling (295)
* [gevent] create a new `Context` when a Greenlet is created so that the tracing context is automatically propagated with the right parenting (287)
* [asyncio] providing helpers and `patch()` method to automatically propagate the tracing context between different asyncio tasks (260 297, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.asyncio) -- thanks thehesiod)
* [aiohttp] add experimental feature to continue a trace from request headers (259, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiohttp) -- thanks thehesiod)
* [django] add `DEFAULT_DATABASE_PREFIX` setting to append a prefix to database service (291, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.django) -- thanks jairhenrique)

**Bugfixes**

* [logging] use specific logger instead of the root one in `monkey.py` module (281)
* [django] `ddtrace` exception middleware catches exceptions even if a custom middleware returns a `Response` object (278)
* [pylons] handle correctly the http status code when it's wrongly formatted (284)
* [django] request resource handles the case where the `View` is a partial function (292)
* [flask] attach stack trace to Flask errors (302)

**New integrations**

* [httplib] add patching for `httplib` and `http.lib`(137 -- thanks brettlangdon)
* [aio-libs] add `aiobotocore` support (257, 298, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiobotocore) -- thanks thehesiod)
* [aio-libs] add `aiopg` support (258, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiopg) -- thanks thehesiod)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.8.5...v0.9.0).
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**Bugfixes**

* [flask] add the http method to flask spans (274)
* [sqlite3] changed the app_type to `db` (276)
* [core] `span.set_traceback()`now sets the traceback even if there's no exception (277)

Read the [full changeset][1].

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.4...v0.8.5
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**Bugfixes**

* [flask] avoid using weak references when Flask is instrumented via Blinker. This resolves initialization issues when the `traced_app = TraceMiddleware(app, ...)` reference goes out of the scope or is garbage collected (273)
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**Improvements**

* [transport] add presampler header (`X-Datadog-Trace-Count`) so that the receiving agent has more information when dealing with sampling (254)
* [docs] updated our documentation (264, 271)

**Bugfixes**
* [core] patch loader raises `PatchException` that is handled in the `patch_all()` when the patch failed. This distinguishes: errors during patch, when an integration is not available and simply when the module is not installed (262)
* [mysql] distinguish `MySQL-Python` instrumentation so that only `mysql-connector` package is patched; this provides better feedback about what library is supported (263, 266)
* [sqlalchemy] provide a `patch()` method that uses the PIN object; this is not a breaking change, but the preferred way to instrument SQLAlchemy is through `patch_all(sqlalchemy=True)` or `patch(sqlalchemy=True)` (261)
* [pylons] catch `BaseException` since a `SystemExit` might've been raised; `500` errors are handled if a timeout occurs (267, 270)
* [pyramid] catch `BaseException` since a `SystemExit` might've been raised; `500` errors are handled if a timeout occurs (269)

Read the [full changeset][1]

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.2...v0.8.3
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**Bugfixes**

* [django] handle tuple `INSTALLED_APPS` for Django < 1.9 (253)

Read the [full changeset][1]

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.1...v0.8.2
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**Bugfixes**

* [core] fixed `msgpack-python` kwarg usage for versions earlier than `0.4.x` (245)
* [pyramid] add request method to Pyramid trace span resource name (249, thanks johnpkennedy)

Read the [full changeset][1].

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.0...v0.8.1
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