filter logging level for Flask sentry middleware
use stacktrace field of Exception interface

Leave `sentry.interfaces.Stacktrace` for non-exception information, e.g.
a client may want to record both exception traceback and the call stack.
raven/contrib/flask/__init__.py: respect the app.config['RAVEN_IGNORE_EXCEPTIONS'] setting to ignore exceptions
docs/config/flask.rst: update documentation on exception filtering
tests/contrib/flask/tests.py: tests for the Flask app.config["RAVEN_IGNORE_EXCEPTIONS"] configuration setting
Merge pull request #371 from razzmatazz/raven-flask-ignore-exception-config

Raven flask ignore exception config
Allow default tag context to be set
pass exception, not the value on failure
Merge pull request #375 from mjallday/gevent

pass exception, not the value on failure
Dont hard error when we are outside of request context
3.5.1
Merge pull request #319 from ianzeng/master

filter logging level for Flask sentry middleware
Fixed the default level value.
Fixed bug in logging.py where messages were not being printed to stderr.
Also took the opportunity to port the print statments in logbook.py to
python3.
Merge pull request #378 from rory-geoghegan-ecometrica/master

Fixed bug in logging.py where messages were not being printed to stderr.
3.5.2
Update base.py

Document captureException kwargs parameter.
Merge pull request #379 from jaraco/master

Update base.py
Fixed linking error
Updated the Django versions.