[Severe] Java 8 - Update Required to support Lambdas

[darylteo]

Currently the Functions are abstract classes, and not interfaces. Due to this, we cannot coerce lambas into functions as they only coerce into Functional Interfaces.

Furthermore, there is a currently a bug in how overloaded methods are disambiguated. Until this is fixed, Java is unable to disambiguate between PromiseAction and PromiseFunction as they both accept Strings but return

In the meantime, 1.2.0 will support the following syntax:

    IRCClient client = new IRCClient(this.vertx, nick, name, result -> {
      this.joinChannels(result).then((PromiseAction<List<Message>>) messages -> {
        System.out.println("WHO: " + messages);
      });
    });

[darylteo]

Apparently the above issue has been fixed. Revisit.