Update changelog.

Handle exc_info=False in logging formatter (mozilla-services#48)

https://docs.python.org/3/library/logging.html#logrecord-objects mentions
exc_info should be a tuple or None, but False can be passed to a log statement
according to https://docs.python.org/3/library/logging.html#logging.debug and
when that happens, the exc_info on the LogRecord object *will* be False as
well, so we need to handle that to avoid crashing.

Python 3.8 support.

More flexible json logger and black/isort.

Django, Python deprecations. Sanic support. Minor fixes.

Minor fix for sqlalchemy and Flask.

Backward-compat fix for Flask migration check.

Doc and logging fixes.

Flask support and minor fixes.

Fixed mozlog message field name to match spec.