Expand normalizeUserAttributeMap

I have refactor method `normalizeUserAttributes` to expand for `normalizeUserAttributeMap` and add example for config client.
Please review. If you think that is reasonable please merge it and complete docs for it.

Thanks
Example is missplaced: explanation about `normalizeAttributeMap` should go along with this field definition.
Full-scale example can be placed at `README.md` if you think it is necessary.