MAINT: update changelog for wrapped facets
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:
+ ```python
+ chart.facet('column_name', columns=5)
+ ```
+ See ``altair/examples/us_population_over_time_facet.py`` for a more
+ complete example.
+
+### Backward-Incompatible Changes
+
+- ``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.
+
## Version 3.0.1
Fix version info bug for HTML output and Colab & Kaggle renderers.
