Precision on the documentation of the Destroy Event

The destroy event is just an internal event since it is thown by the
killMe method and to be able to call this method a super-holon must have
any member, so it is not necessary to wake this event but just inform
internal behaviors not members ones.
Correction of potential null keys Addresses' collection and use of set instead of collection

This commit solves the issues related to null pointer exceptions in
collection.
And introduce set in place of collection to manage scope of addresses.
Issue #39
Issue janus-project/janusproject#21
Issue janus-project/janusproject#22