There's a good chance that this will be evtclib 0.5, so we want to adapt
our API usage (mainly replacing evtclib::Boss with evtclib::Encounter).

The naming is a bit all over the place now, as we sometimes refer to
bosses and sometimes to encounters, but I hope to make a sensible
decision at *some point* about what we're actually doing here.

This is better than re-implementing these functions, especially for the
fight outcome as it is more accurate.

It makes sense to unify this implementation to avoid code duplication
and bugs that might be hidden. -after and -before can stay for now, as
shortcuts for -time < and -time >, the same way we have other shortcuts
as well.