Release v0.5.0

This is the first tagged release of this package. It is already in use in a number of packages, and arguably a tagged release should have been made much earlier. This release does not represent any recent significant changes, only the documentation has been improved in some places.

In my opinion, the core structure and public interface of the package have proven themselves fit for purpose. Ideally, I will at some point find the time to iron out some of the rougher edges of the package in an entirely backwards-compatible manner. When I have achieved this goal, I expect to release a stable 1.* version.