Enhancement: register a function to every signal

[premek]

I'd like to be able to register a function that will be called with every 'emit'. I'd use that to call 'print' with every signal to have a log of events. e.g:

Signal.register(function(...) print("signal emmited", ...) end)

[palmettos]

I thought this was a good idea so I created a pull request here: #78

With this feature you would do:

signal.registerPattern('.*', function(...) print('signal emitted', ...) end)