Added a new section to the FAQ about changing post CSS by category slug.

git-svn-id: https://plugins.svn.wordpress.org/editorial-calendar/trunk@903231 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated the stable tag to 3.1.1.

git-svn-id: https://plugins.svn.wordpress.org/editorial-calendar/trunk@903232 b8457f37-d9ea-0310-8a92-e5e31aec5664