Adjustment for scoping

The code was wrapped in two anonymous functions, which could cause `this` to be undefined depending on how the loglevel code was included in a project. 

Only using one anonymous function and having this be at the "top-level" allows the code to be wrapped and invoked with apply like so:

```javascript
var myScope = {}:
(function(){
 // loglevel.js source
 // "this" will equal myScope, since the "this" in loglevel.js is in this scope.
}).apply(myScope);
myScope.log.debug("log was defined on myScope");
```

The code change follows the same pattern as this:
https://github.com/marionettejs/backbone.marionette/blob/master/src/build/marionette.core.js

I'd love to write a unit test but I'd have to adjust the `Gruntfile.js` and include grunt-preprocess or grunt-rigger, which are code injection/include tools, to generate a test that includes the `loglevel.js` wrapped in a function invoked with apply. If you want me to do this I will. 

I also hope that my change doesn't affect anything that the `undefined` argument was doing.
https://github.com/pimterry/loglevel/blob/master/lib/loglevel.js#L8

Thanks,
Gianni
Sure, it's an integration test for that functionality, with a version of a major popular library for which it breaks. This is all irrelevant to this PR though; I don't think either of us want to include these changes, so can you please pull them out, and then I'll merge this.

Feel free to add some noConflict unit tests too in another PR if you'd like, I'm fine with that, but let's get the unrelated and useful functionality from this PR merged in first please.