C++ Network Library Code

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.

Refactoring URL parser to introduce better support for RFC; increasing C++ template depth to 256.