Update to PEP308: if-then-else expression

[Raymond Hettinger]

I updated the PEP for Guido van Rossum.

If the cron job is doing its thing, the results will be visible in
a few hours.

The update reflects updated thinking based on the discussion to-date.
It also summarizes a few posts from comp.lang.python.
Hopefully, it will serve to focus the discussion on the
best of the ideas and arguments presented so far.

* Out of order evaluation is out of favor.

* So are ideas that do not provide for short-circuiting.

* (if <condition>: <expression1> else: <condition2>) is in vogue.

* <condition> ?? <expression1> || <expression2> is a new contender.

* cond(<condition>, <expression1>, <condition2>) is viable if implemented
      as a keyword and has short-circuit behavior.  Note, the actual word
      is still an open question.  iif() got shot down quickly.

* Added a summary of a few ideas from the last couple hundred posts
      from comp.lang.python.


Raymond Hettinger