Update Myth to v1.1.1

There have been quite a few changes to the proposed CSS specs (i.e. the vars syntax), and these are reflected in a major new version of Myth. This pull request updates the fallback myth.js to that latest version (v1.1.1).

Unfortunately, updating Myth to the latest version will likely throw errors for anyone not pointing to a local install of myth.js… is upgrading the fallback to the latest version okay with you? Is there a better approach?