Merging changes from Git for 0.0.4 release

git-svn-id: http://plugins.svn.wordpress.org/wp-pjax/trunk@690329 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added screenshots in Assets folder. Fixed bug with sitemap URL in default settings
Updated changelog and changed version numbers
Added screenshots in Assets folder. Fixed bug with sitemap URL in default settings