Adding XML layout for blog tags to render properly.

[mshaver]

This adds the XML layout needed to render the tags in feed readers.

[mshaver]

@heypaxton do you mind looking over this PR. It looks like the feed works fine in a reader, but many of the variables don't actually render, so it's a little hard to tell if they should just be pulled out or not.

[heypaxton]

This looks good, @mshaver. Some of the fields may not render because some of them are optional, such as the author name.