Porting Perl examples to use ZMQ::LibZMQ3

I've ported all the existing examples of Perl code to use the new version of the lib - `ZMQ::LibZMQ3` - (up from `ZMQ::LibZMQ2` or even `ZeroMQ` in one particular instance).

I tried to stay close to the previous examples, but when possible I have used the `zhelper.pm` lib to get a little bit closer to the examples in C.