Prepare for 3.2.4
In this MR:
- Some (dummy) comments added to make doxygen happier
- Update of the Pythia6 interface
- Formatting
- Reorganize the list of dependencies used for tests. Valgrind is switched off by default.
From what I see even the latest fixes don't help to avoid false-positive messages from valgrind.
In the same time the valgrind is explicitly enabled in CI with
-DHEPMC3_TEST_VALGRIND:BOOL=ON
and theglibc-debuginfo
package is provided. This change allows to have builds for all Fedora architectures. Tag @ellert in case there is an idea for a better solution.