Lift methods for Aggregator and MonoidAggregator

This can be useful when you have a common call site that expects to use
the standard Aggregator API (prepare, present) but in some cases you
wish to aggregate values that come as Option or collection types.
This affects all of prepare, present and semigroup, so I don't see how composePrepare could achieve it. As an example `MinAggregator[Double].lift` gives you an `Aggregator[Option[Double], Option[Double], Option[Double]]`. How else would you do that succinctly?