I need a make a decision as to what (if anything) belongs in imp and then document what stays and deprecate everything else.

Everything in imp falls into one of the following categories:

* From importlib
  - get_magic()
  - source_from_cache()
  - cache_from_source()
* From sys
  - get_tag()
* Platform-implemented
  - lock_held()
  - acquire_lock()
  - release_lock()
  - Undocumented stuff related to builtins, frozen, and load_dynamic()
* Helper
  - reload()

The question is what to keep/expose in imp and what to deprecate. Basically I need to figure out what imp's role is supposed to be in the face of importlib. My gut says either expose platform-dependent stuff and reload() and move the rest to importlib/deprecate, or to completely do away with the module and force people to use the APIs in importlib for consistency (and to stop people from mucking around with import from outside of importlib).