Support creating timezones by numeric-string codes.

[Dan Strohl]

For example, when I do a dt.strftime('%z'), I get a string '+0800', when I look at log entries with time zones, I often see '+0800' (or similar). Right now, I parse those into hour/minute/second data, than convert them to a python timezone object... but then I may need to handle them differently since the python object doesn't have the localize method.

It would be nice to simply be able to do something like pytz.timezone('+0800') and have it return a pytz object for that offset. Understanding that it would not know where in the world it was or handle daylight savings time.

Alternativly, how about the ability to convert a python timezone object to a pytz one?