Costumizable file path

Hi! I've used your code in my IRC bot, but I made a little change along the way and thought I might as well send it back your way for you to use if you feel like it.

It basically allows the coder to set the path and name of the json file either dynamically at object instantiation, or by extending the class -- in either case, without having to change the file itself, thus allowing future git pulls without conflicts. If no file is specified, it just looks for a storage.json file in the same directory as the class file (which appears to be the default intended behaviour).