Brings single author links into hcard compliance

Google now looks for structured data on pages (lacking that data is considered an error by Webmaster Tools). These changes bring Co-Authors-Plus's output in-line with the hAtom hCard microformat for authorship.

There is one downside with this configuration. Strictly speaking the `fn` tag in the link's class designates formatted/full name, which may not be the case depending on the user's configuration. The `fn` tag is required and the output of `get_the_author` may not be full, but it is highly unlikely that it is not at least formatted, so I feel safe in this setup. Further, this can be filtered by the user if the specific use is out of standard.

For reference:
More info about Google's use of structured data for rich snippets is at https://support.google.com/webmasters/answer/1093493?hl=en

The hAtom spec is at http://microformats.org/wiki/hatom

The hCard spec is at http://microformats.org/wiki/hcard