date template tag should support "e" and "o" format character

[Carsten Fuchs]

The date template tag currently supports the "W" (ISO 8601 week number) format character, but not the complementing "o" (ISO 8601 year number machting the ISO week number) character.

Both are described at the documentation that the date template tag is referring to:
​http://de2.php.net/manual/en/function.date.php

A workaround is possible with a custom template tag, returning the result of datetime.strftime("%G").

[Aymeric Augustin]

Here's a list of the differences between what PHP supports and what Django supports:

b => added in Django
B => not implemented in Django
E => added in Django
e => not available in Django, added in PHP 5.1.0
f => added in Django
I => not implemented in Django
N => added in Django, added in PHP 5.1.0 with a different meaning
o => not available in Django, added in PHP 5.1.0
P => added in Django, added in PHP 5.1.3 with a different meaning

We should implement e and o, or mention in the docs that they're not implemented, like B and I.

Also, iven the divergence of N and P, maybe we could drop the reference to PHP from the docs.

[Jannis Leidel]

In [17473]:

Fixed #16416 -- Added two new date formatting options for timezones and ISO week numbers. Thanks, poirier.