update CHANGELOG and bump version to 3.0.0

Signed-off-by: Benjamin Wohlwend <beni@elastic.co>

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

 - introduced consistent logger name scheme for all elasticapm intern…

…al log messages (elastic#212)

  - added instrumentation of cassandra-driver (elastic#205)
  - added instrumentation of elasticsearch-py (elastic#191)
  - added Flask 1.0 to the test matrix (elastic#207)
  - fixed an issue with our minimalistic SQL parser and "fully qualified" table names (elastic#206)
  - fixed issue with spans in Django’s `StreamingHTTPResponse` not being captured (elastic#201, elastic#202)
  - fixed issue with spans with Flask’s streaming response not being captured (elastic#201, elastic#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 D…

…jango 1.10 or 1.11 while using the MIDDLEWARE_CLASSES setting (elastic#186, elastic#187)

* fix an encoding issue with log messages that are hit in rare cases (elastic#188, elastic#189)

**v2.1.0**

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

- fixed compatibility issue with aiohttp 3.0 ([\elastic#157](elastic#157

))

- Added truncation for fields that have a `maxLength` in the JSON Schema ([\elastic#159](elastic#159))

updated changelog and bumped to v2.0.0

version bump to 1.0.0

version bump to 1.0.0.dev3

bumped version to 1.0.0.dev2 and updated Changelog