Add Optional methods that does not breaks chaining

[aNNiMON]

Currently, ifPresent returns void and breaks chaining. For convenience sake I'll add these methods:

Optional executeIfPresent(Consumer c)
Optional executeIfAbsent(Runnable r)

Optional.ofNullable(result)
    .executeIfAbsent(() -> error("Empty result"))
    .or(() -> Optional.ofNullable(anotherResult))
    .executeIfAbsent(() -> error("Still no result"))
    .executeIfPresent(this::processResult);