2.99.5 (unstable):

* Functors (mem_functor, ptr_functor) no longer need to derive from a common
  functor_base base class, and functors no longer need to have a result_type
  typedef or alias.
* emitters and accumulators no longer need t ohave a result_type typedef or
  alias.
* Remove now-unnecessary adaptor_type type aliases.
* Remove some more unused and unnecessary public type aliases.