Incorrect filter code conflicting with other plugins

While investigating an issue with a site I maintain, which uses your plugin, in which social buttons added by a different plugin were failing to appear, I narrowed down the cause of the problem to the the_content filter that your plugin registers. Instead of simply modifying the $content variable that is passed to it, as is documented here, your plugin instead makes its modifications directly to $post->post_content, effectively destroying any changes made by previously-run filters (which, incidentally, is nearly all of them, since you set a filter priority of 20 for some reason). Here is a patch which corrects the filter.