Add logger

[olleharstedt]

Logging should not be done by directly calling console.log, but by a proper logging class with logging levels as debug, trace and error. This should be able to turn off in production system.

[olleharstedt]

I'm using this logger in my fork now: https://github.com/jonnyreeves/js-logger

[Lukenickerson]

I've been hesitant to bring in additional libraries because I'm not sure how they play well with the license. This might be something worth looking into.

[olleharstedt]

The logger uses MIT, which is more permissive than GPL, so it should be OK, I think.