Set debug as instance attribute

[jacopoabramo]

Hey, great project.

Not really sure if this is still actively mantained but this PR sets self.debug in the elliptect.controller.Controller class.
In some code sections it is referenced, but when using the controller, AttributeError is raised due to the fact that the local attribute is not declared in the first plase.

As a tip, you should probably consider setting up a Logger instance rather than using prints, since it's more intuitive and doesn't require to pass a debug flag which instead you can control directly by setting logging.setLevel("DEBUG"). But it's out of scope of this PR

[roesel]

Valid change and valid comments. I keep this library available, but I definitely cannot say it is "maintained", since I no longer have time to invest into it. Therefore, it remains in a "just barely works" state where it was when I was leaving the lab in which I wrote this :)

I appreciate the PR. If you have anything more substantial in the future, please do not hesitate to make a PR, I would love for the library to keep improving!