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.
Merge pull request #754 from sinisterstuf/about.com

Add support for *.about.com