By-author pages

[mist64]

We should have a page for every author

• which is reachable by clicking at the author name at the end of an article.
• which lists all articles written by the author, sorted by issue and page.

(Later: Pick up an HTML file (e.g. subdir "authors") per author with a bio, maybe a picture, and add it to the author page.)

[ellduin]

when adding this also add the author url to the article information (see #85)