* 1:     Mentioning interaction with foreign threads as an open problem.
* 2 & 3: Removed `threadsafe' again, as the proposal for thread support is
         still evolving and it is not yet clear whether a new safety level
         is required.
* 5.5:   Added the type synonym `FinalizerPtr' and rewrite the documentation
         of finalizers.
* 5.6:   Clarified the description of `StablePtr'
* 5.8:   Added `finalizerFree'
* 6.2:   All the types in CTypes must be newtypes that are exported
         abstractly.