Change log

Next version

Added a spark.api.event helper for creating events.
Moved all imports in the spark.api module into the functions using them so that the module can always be imported early during startup.
Decoupled the generators API from Generator model instances. Documentation will be written after some additional real world testing. events_from_generators now accepts a list of generator descriptions instead of a generator queryset. The .as_generators() queryset method easily allows creating a suitable generator description.
Separated EmailMessage generation from sending in the spark_mails API and made mail sending not fail silently by default.
Fixed a bug where an empty template would crash the mail rendering.
Rewrote the Travis CI configuration to make jobs explicit, added newer Django and Python versions to the matrix.

Changed API events to be dictionaries instead of types.SimpleNamespace objects. The top level of the dictionary normally contains key and group keys used by django-spark and an additional context dictionary with arbitrary data.
Added a new Event.objects.create_if_new queryset method which understands event dictionaries.
Added a new spark.spark_generators app for configuring spark generators using Django's administration interface.
Changed the API contract for sources and sinks: Sources and sinks are both NOT responsible for only letting new events through. A new spark.api.only_new_events filtering iterator has been added which only yields events that haven't been seen yet.
Added a new spark.spark_mails app for transactional mails.