struct for URI representation fixes

New branch, changes to pull request #2257
1. Some methods removed.
2. Parsing algorithm changed from regexp to string slicing (by @s-ludwig)
3. proprety "auth" renamed to "userInfo"
4. Examples converted to documented unittests
This still isn't any different from assigning to `URI.init`. It's just another name for a fundamental operation, so we should do without it.