[Python-3000] Latest revision of PEP 3101

[Talin]

You can find it in the usual place:

     http://www.python.org/dev/peps/pep-3101/

There are no changes to public APIs, the only changes are to the 
extension mechanism for custom formatting classes. Also, I've edited a 
lot of the text in order to improve the clarity of explanations and cut 
out excess verbiage.

Comments are welcome as usual.

-- Talin