Raise requirements to 2.8

git-svn-id: https://plugins.svn.wordpress.org/libravatar-replace/trunk@936193 b8457f37-d9ea-0310-8a92-e5e31aec5664
add readme.md and license

git-svn-id: https://plugins.svn.wordpress.org/libravatar-replace/trunk@936194 b8457f37-d9ea-0310-8a92-e5e31aec5664