heyoka 0.8.0

This new release of heyoka features a couple of breaking changes in the event detection API. The changes are explained in detail here:

https://bluescarni.github.io/heyoka/breaking_changes.html#bchanges-0-8-0

The release contains also a couple of new features for the propagate_*() functions and a bugfix in the event detection system. As usual, the full changelog is available here:

https://bluescarni.github.io/heyoka/changelog.html