v0.4

This is a major release that includes a number of new features and bug fixes, including several changes from existing behavior.

Highlights include:

• Automatic alignment of index labels in arithmetic and when combining arrays or datasets.
• Aggregations like mean now skip missing values by default.
• Relaxed equality rules in concat and merge for variables with equal value(s) but different shapes.
• New drop method for dropping variables or index labels.
• Support for reindexing with a fill method like pandas.

For more details, see the release notes.