Added connection events and removed connections array

I've made a number of changes to the package to make it more useful for one of my current projects.
The include the ability to have functions called upon connection or disconnection and using the mongo collection to manage the presence of the logged or anonymous user.

Unfortunately I didn't really have time to build test, but the console.log statements do get fired when I expect.

As, the pr is a departure from your existing approach I expect that you dismiss it. I won't be offended or anything, I just figured on the off chance that it be useful for you it's there.

Thanks for you efforts.
Marc