Refactored traits from message so it might be easier to reuse them.
Refactored traits and tags so that they are not duplicated for message and URI.
Merged 71-HEAD from branches/urllib-dean
Updated some more docs. They're not complete and still need reviewed.
Supporting +,-, and . in the scheme part as per RFC 1738.
Adding uri example.
Implementing basic_uri constructors that take a string as a parameter.
minor cleanup
adding userinfo to structural parsing
Renaming files and implementations from URL to URI.
