Switch to using node-config

I am proposing a switch to using [node-config](https://github.com/lorenwest/node-config).  Although its adding a new dependency to Glog, I think that it will also add a lot of benefit, by abstracting out config handling and allowing much more fine grained control over configuration.

The downside is that the name and location of the config file need to be changed to config/default.json and therefore would have to mark a major version in Glog.

I have submitted the proposal on the config branch (shown in this pull request).