* 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.
