Add support for *.about.com

Includes `next_page_link` for multi-page articles and strips pesky in-line
'next' links from the article body. Also includes an Xpath for author
but I can't see where this is used in the wallabag UI.

The `tidy` option is turned off because it messed up bulleted lists.

Tested with psychology.about.com and food.about.com.