This required a few further additions to the TokenTransformDispatcher. In
particular, there is now an 'any' token match whose callbacks are executed
before more specific callbacks. This is used by the Cite extension to eat all
tokens between ref and /ref tags. This need is very common, so should be
broken out to an intermediate layer in the future.
In general, the requirements for the TokenTransformDispatcher API are now
clearer, and the API should likely be cleaned up / simplified.
