MuPlusLambdaBreeder is a subclass of MuCommaLambdaBreeder which, together with
ESSelection, implements the (mu + lambda) breeding strategy and gathers
the comparison data you can use to implement a 1/5-rule mutation mechanism.
Note that MuPlusLambdaBreeder increases subpopulation sizes by their mu
values in the second generation and keep them at that size thereafter.
See MuCommaLambdaBreeder for information about how to set mu and lambda.