Make initialisation simpler and independent of a newrelic.js config file

From #27

The rationale is that [nodetime](http://nodetime.com) and [nodefly](http://nodefly.com) have super simple copy paste setup for their profilers, so why shouldn't new relic?

Now it is possible to startup newrelic by inserting the following at the top of your app:

    require('newrelic').profile({
        app_name: 'your_app_name',
        license_key: 'your_license_key',
        <other options>
    });

Big thanks to you guys for extending your support to node.js! nodetime and nodefly are okay, but they just don't compare to newrelic's awesome power.