2.5.10 Maintenance release; legacy code removal

git-svn-id: https://plugins.svn.wordpress.org/google-document-embedder/trunk@804474 b8457f37-d9ea-0310-8a92-e5e31aec5664
2.5.11, disabled beta api removed; import fix

git-svn-id: https://plugins.svn.wordpress.org/google-document-embedder/trunk@804688 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme.txt update (no code changes)

git-svn-id: https://plugins.svn.wordpress.org/google-document-embedder/trunk@804818 b8457f37-d9ea-0310-8a92-e5e31aec5664