Opbeat

* Fixed bug in Redis instrumentation introduced in 3.1 refactor.

* Flask APM support. Install as opbeat[flask] to ensure flask deps are installed.
* Introduce opbeat.trace decorator for better insights into custom code
* Internal refactoring to support the decorator.
* Stop instrumenting pipelined Redis operations.

* Only log one line per module we failed to instrument

* Fix a problem that occurs when `end_transaction` gets called twice in a row
* Silently ignore `DatabaseError` when collecting user info for Django.
* Better error logging with `async=True`
* Renamed `async` keyword in anticipation of Python 3.5+
* Instruments Django middleware by default to give better insights in APM
* Better sanitation of http body
* A bit of cleanups and refactoring

* Fix a bug in trace reporting that occurred if the traced code would raise
* Introduce a management command to test out local Opbeat configuration and
send a test exception.
* Include templates in stackframes in traces.
* Various bug fixes related to stackframes in traces.

* instrument python-memcached
* Make sure only one of urllib3 and requests will show up on traces