Add support for Django 2.0 (#176)

Fix saving viewflow tasks with formsets (#175)

1.1.2

* Switch to pbr
* Switch to codecov
* Switch README to ReStructuredText

Version 1.1.1

* Fix svg target

Version 1.1.0

- Add support for bpmn to flow_graph command
- Change sphinx implementation

Release 1.0.1

- Fix possibility to save tasks with empty required fields

Update django-viewflow to 1.12

Fix viewflow-pro Obsolete node import error

 - Add sphinx extension that renders BPMN from flow using graphviz

 - Add django-admin command that renders BPMN from flow using graphviz

Improve documentation