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