Show index of circular references and trim of code to 80 columns

The index could allow to identify what's the instance that is doing the circular reference (maybe in the future could be added support to set a reference to it when decoding the object, maybe exporting someway the list of seen objects).

The limit to 80 columns makes it easier to read the code, I didn't do it on the regular expresion but it would be also possible setting it by a string and a RegEx object constructor.