I'm pleased to announce that the Moodle 2.2 English documentation wiki is now available - docs.moodle.org/22/en/ including documentation of new features in Moodle 2.2. Thanks to everyone who has helped.
You'll find that 'Moodle Docs for this page' links in Moodle 2.2 redirect to the 2.2 documentation, the same as links in Moodle 2.1, 2.0 and 1.9 redirect to the appropriate version wiki.
If you visit Moodle Docs you'll notice it has a new theme, designed to save screen space and make it easier for users with mobile phones and smaller screen sizes to access the documentation. Blocks previously in the left column can now be found in the footer, and a new navigation bar above the page tabs will hopefully help people to navigate the documentation more easily. Thanks to Sam Hemelryk for developing the new Moodle Docs theme.