v0.16.1

This is a small hot-fix release to update dependent Rust polars to 0.39.1 (#1042).

Also, there are some updates.

Bug fixes

• $len() now correctly includes null values in the count (#1044).

Other improvements

• $arr$max() and $arr$min() work without the nightly feature (#1042).

Full Changelog: v0.16.0...v0.16.1