New API suggestion: ifLeft, ifRight

[soerenBoisen]

Optional has method ifPresent to consume the value, if it is present. It would be useful to have the equivalent methods ifLeft and ifRight on Either.

Right now I'm doing this, which is laborious:

either.left().toOptional().ifPresent(left -> doStuff(left));

Instead I would like to do:

either.ifLeft(left -> doStuff(left));