[Python-3000] PEP - string.format

[Talin]

I decided to take some of the ideas discussed in the string formatting
thread, add a few touches of my own, and write up a PEP.

http://viridia.org/python/doc/PEP_AdvancedStringFormatting.txt

(I've also submitted the PEP via the normal channels.)

I don't have a prototype, however the PEP is explicit enough about the
details of operation that a prototype should be fairly straightforward.

-- Talin