Updated readme, plugin header file, and pot file to version 1.2.1.

git-svn-id: https://plugins.svn.wordpress.org/instant-breadcrumbs/trunk@846627 b8457f37-d9ea-0310-8a92-e5e31aec5664
Switched stable tag to 1.2.1.

git-svn-id: https://plugins.svn.wordpress.org/instant-breadcrumbs/trunk@846629 b8457f37-d9ea-0310-8a92-e5e31aec5664