Elastic-apm

* added sanitization for `Set-Cookie` response headers (264)
* added instrumentation for the non-standard `Connection.execute()` method for SQLite3 (271)
* added "authorization" to list of sensitive keywords, to ensure that "Authorization"
HTTP headers are properly sanitized (275)
* taught the Logbook handler how to handle the `stack=False` option (278)
* fixed a race condition with managing the timer-send thread (279)

- adapted "black" code formatter for this repository (262)
- **BREAKING**: dropped support for Python 3.3 (242)
- **BREAKING**: changed order of precedence when evaluating configuration (255, 261)
- **BREAKING**: changed default value of `span_frames_min_duration` setting
from `-1` (always collect) to `5` (only collect for spans longer than 5 ms) (243)
- added instrumentation for pymssql (241)
- added instrumentation for pyodbc (238)

- fixed an issue with Django Channels (232, 233)

- introduced consistent logger name scheme for all elasticapm internal log messages (212)
- added instrumentation of cassandra-driver (205)
- added instrumentation of elasticsearch-py (191)
- added Flask 1.0 to the test matrix (207)
- fixed an issue with our minimalistic SQL parser and "fully qualified" table names (206)
- fixed issue with spans in Django’s `StreamingHTTPResponse` not being captured (201, 202)
- fixed issue with spans with Flask’s streaming response not being captured (201, 202)

**NOTE**: This will be the last release with support for Python 3.3.

- fixed bug in Django management command that would be triggered on Django 1.10 or 1.11 while using the `MIDDLEWARE_CLASSES` setting (186, 187)
- fix an encoding issue with log messages that are hit in rare cases (188, 189)

- made skipping of initial `elasticapm` frames for span stack traces more generic ([\167](https://github.com/elastic/apm-agent-python/pull/167))
- added `context.process.ppid` field (supported in apm-server 6.3+) ([\168](https://github.com/elastic/apm-agent-python/pull/168))
- added option to disable stack frame collection for very short spans ([\142](https://github.com/elastic/apm-agent-python/pull/142))
- several bug fixes:
- fix an issue in boto3 instrumentation with nonstandard endpoint URLs ([\178](https://github.com/elastic/apm-agent-python/pull/178))
- fix bug with OPTIONS requests and body capturing ([\174](https://github.com/elastic/apm-agent-python/pull/174))
- fix issue when message has `%` character, but no params ([\175](https://github.com/elastic/apm-agent-python/pull/175))