Fix author links - Githubissues

Currently all links to author mentions just go to back to the the homepage of the site:

On our example site "dennis" is an author that has a profile page defined, however when you click on the name, it just goes to back to the homepage.

Now that we have good support for Author listings/profile pages, we should properly link to the actual author profile if it exists.

Things to consider:

[x] how do we detect if an author has a profile filled out?
[x] what should we do if author does not have profile? my guess is we should just not have a link at all.
[ ] we should probably move this into its own partial so that we can just reuse this little author linking logic.

dencold / hasper