Moved CheckingEqualizer, Equalizer, and LegacyEqualizer into EqualityConstraints, to get it out
of sight in the Scaladoc scalautils package list.
Renamed TripleEqualsConstraints to TripleEqualsSupport and TripleEqualsConstraint to TypeConstraint; moved AToBEquivalenceConstraint,
BToAEquivalenceConstraint, DecidedByEquality, DeterminedByEquivalence, and LegacyCheckingEqualizer into TripleEqualsSupport so they
don't show up in the Scaladoc for scalautils.