Update includes full compatibility with version 3.3 of Vega-Lite.

Enhancements

Added support for vega themes via alt.themes.enable(theme_name) (#1539)
Added an alt.renderers.disable_max_rows() method for disabling the maximum rows check (#1538)
Improved user-facing warnings/errors around layering and faceting (#1535).
data argument is now properly handled by Chart.properties (#1525)
Compound charts (layer, concat, hconcat, vconcat) now move data to the top level by default. In particular, this means that the facet() method can now be called directly on a layered chart without having to change how data is specified. (#1521)
alt.LayerChart now supports mark_*() methods. If a layer specifies a mark at the top level, all child charts will inherit it (unless they override it explicitly).
alt.Chart.facet() now handles wrapped facets; for example: chart.facet('column_name', columns=5) See altair/examples/us_population_over_time_facet.py for a more complete example.

Bug fixes

Make chart.serve() and chart.save() respect the data transformer setting (#1538)
Fixed a deserialization bug for certain chart specs in schemapi (#1543)

alt.Chart.facet() now accepts a wrapped facet encoding as a first positional argument, rather than a row encoding. The following are examples of old invocations, and the equivalent new invocations:
chart.facet(row='col1', column='col2'): unchanged
chart.facet('col1', 'col2'): change to chart.facet(row='col1', column='col2')
chart.facet('col1'): change to chart.facet(row='col1')

In each case, the new invocations are compatible back to Altair 2.X.

Several of the encoding channels added in 3.0 have had their capitalization corrected to better match the names used in the schema:
alt.Fillopacity -> alt.FillOpacity
alt.Strokeopacity -> alt.StrokeOpacity
alt.Strokewidth -> alt.StrokeWidth
alt.Xerror -> alt.XError
alt.Xerror2 -> alt.XError2
alt.Yerror -> alt.YError
alt.Yerror2 -> alt.YError2