Hot-fix - xarray v0.12.0 breaking changes

Quick release to align with breaking changes made in xarray v0.12.0, namely dropping Python 2 support.

Hot-fix v0.3.4

This is a hotfix release before pushing ownership of the repository.

Hot-fix v0.3.3

Includes some small tweaks to work with 3D output fields and compatibility for xarray v0.10.2.

v0.3.0

Release xbpch with official mirror on PyPI and updated documentation.