Document the `show_admin_column` argument

[johnbillion]

The show_admin_column argument which was added to register_taxonomy() in 3.5 is not documented and does not have a default value.

[johnbillion]

Patch

[DrewAPicture]

This and many other functions are in line for converting the $args array docs to a hash notation, 26707.diff​ looks good for now though. Thanks.

[DrewAPicture]

In 26912:

Add inline documentation for the 'show_admin_column' argument added to register_taxonomy() in 3.5.

Also adds a 'show_admin_column' value to the defaults array.

Props johnbillion.
Fixes #26707.

[DrewAPicture]

@johnbillion:

Reflecting on [26912], adding the default is obviously very "codey" and not so much on the "documenting-ey", just want to make sure that that value is indeed supposed to default to false, as we obviously enable it for both categories and tags out of the box.

[johnbillion]

Correct, the show_admin_column argument is false by default.

It's set to `true` for categories and tags and then only taxonomies which set it to true are displayed on post listing screens and media listing screens.