Merge pull request #14 from mafagafogigante/master

Small refactorings
simplified toString method
accepted suggestion note by @iluwatar
Merge pull request #15 from noragami/master

simplified toString method
Added example of generic observer
Added message to observer app
Added Java Generics and Collections to credits of readme
Merge pull request #16 from joningis/generic-observer

Generic observer
Update README.md
Update README.md