Update readme to reference new library files.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@870439 b8457f37-d9ea-0310-8a92-e5e31aec5664
Remove empty library directories.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@870441 b8457f37-d9ea-0310-8a92-e5e31aec5664