This is a rather long commit, because it refactors lots of the event
code from pointer to value semantics: pointers to entries in an
std::vector<> are not stable, so better use indexes.
To step through the event-list at diven time stamps, add *_loop classes,
which encapsulate state that had to be manually handled before by
the caller. I'm not happy about the interface, but it tries to
mirror the one we had before.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
