heyoka 0.6.0

This new version of heyoka comes with a big new feature, event detection. A tutorial chapter describing the new feature is available here:

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

Another important new feature is that propagate_grid() can now be used with the batch integrator.

The full changelog is available here:

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