Version 0.3.0

Behavior changes

• save() now returns the serialized chart if fp is not specified (#41).
• fmt="json" now saves the input spec directly for both vega and vega-lite input.
  Additionally, the json format in render() outputs a JSON mimetype rather than
  a vega-lite mimetype (#34).
• render() and save() with HTML format now have a standalone argument
  that defaults to True for save() and False for render(), so that HTML
  output will work better in a variety of notebook frontends (#33).
• HTML and Selenium output now respects embedding options set via
  alt.renderers.set_embed_options (#30, #31).

Maintenance

• much improved documentation & test coverage.