[Python-3000] Substantial rewrite of PEP 3101

[Talin]

I've rewritten large portions of PEP 3101, incorporating some material 
from Patrick Maupin and Eric Smith, as well as rethinking the whole 
custom formatter design as I discussed earlier. Although it isn't 
showing up on the web site yet, you can view the copy in subversion (and 
the diffs) here:

    http://svn.python.org/view/peps/trunk/pep-3101.txt

Please let me know of any errors you find. Thanks.

-- Talin