* TokenTransformDispatcher is now renamed to TokenTransformManager, and is
also turned into a base class
* SyncTokenTransformManager and AsyncTokenTransformManager subclass
TokenTransformManager and implement synchronous (phase 1,3) and asynchronous
(phase 2) transformation stages.
* Communication between stages uses the same chunk / end events as all the
other token stages.
* The AsyncTokenTransformManager now supports the creation of nested
AsyncTokenTransformManagers for template expansion.
The AsyncTokenTransformManager object takes on the responsibilities of a
preprocessor frame. Transforms are newly created (or potentially resurrected
from a cache), so that transforms do not have to worry about concurrency.
* The environment is pushed through to all transform managers and the
individual transforms.
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.
