Incremented version number.

Added to readme: We will soon be releasing a beta version of PowerPress 6.0. If you are interested in beta testing, please [contact us](http://www.blubrry.com/contact.php).

git-svn-id: https://plugins.svn.wordpress.org/powerpress/trunk@930541 b8457f37-d9ea-0310-8a92-e5e31aec5664