Cleaned up traits subdirectories.
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
