Improve categories/tags in ATOM feeds

[andy]

Currently we do not differentiate between categories and tags, and we combine them if a post has the same term in both taxonomies.

<category scheme="http://myblog.com" term="Cats" />
<category scheme="http://myblog.com" term="Dogs" />

Attached patch adds support for permastruct-based category schema, uses term->slug for term and term->name for label.

This way, you can construct the category/tag URL from the scheme+term. Here is sample output:

<category scheme="http://myblog.com/category/" term="cats" label="Cats" />
<category scheme="http://myblog.com/category/" term="dogs" label="Dogs" />
<category scheme="http://myblog.com/tag/" term="dogs" label="Dogs" />

Support for custom taxonomies remains a problem for plugins to solve.

#8828 attempts to fix the same issue.

broken patch

Closing this as the duplicate of #8828.