heyoka 4.0.1

[bluescarni]

This is a quick release that fixes a build issue on PPC64.

NOTE: heyoka 4.x introduces several breaking changes with respect to the 3.x series. Please see the following link for a list of breaking changes and explanations on how to adapt your code to the new API:

https://bluescarni.github.io/heyoka/breaking_changes.html#bchanges-4-0-0

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This discussion was created from the release heyoka 4.0.1.