Factored out source code analysis logic (for capturing angular module dependencies)

I needed the portion of code that analyze the angular module dependencies, so I created a different NPM module for it https://github.com/blai/ng-dependencies. I also fixed a couple of use cases, see the [unit tests](https://github.com/blai/ng-dependencies/blob/master/test/index_test.js) for detail.

Would you allow me to hand over the ownership of https://github.com/blai/ng-dependencies back to you? (since the source code were yours anyway).

By the way, would it be possible for the sorting algorithm not depend on `relative` of `file`, but purely on `file.content`? (https://github.com/klei/gulp-angular-filesort/blob/master/index.js#L55 and https://github.com/klei/gulp-angular-filesort/blob/master/index.js#L73), this way we can also factor out the sorting logic (I found other purpose of using it a little differently).