Added logLevel configuration option

I like the library a lot, but it's hard to see you own debug messages when there are those from smokesignal popping up all the time. I added a few lines of code, that add a configuration option to the `node({config})`, that will just call the default `log4js.setLevel` method and change it to the chosen one. 
I don't know if that is what you ment in your `README.md@TODO` but I think that would be a nice addition for the tool.