Code review

@cableman I think this looks sound and the readme is very nice.

Somewhat related but out of scope for this PR I would like to suggest that we in general switch away from Features  to [Secure Permissions](https://drupal.org/project/secure_permissions) for managing roles and permissions.

In my experience Features is unusually buggy about handling permissions with problems regarding status and reverting them. We have not experienced these problems with Secure Permissions and I agree with the general purpose of the module as well.

//cc @mikl.