- Add methods to registry that do the lion's share of the various jobs
  currently performed by ZCML directives.  Change existing ZCML
  directives to use these methods of the registry.

- Emit a set of events at startup that calls an event listener with
  the registry before and after ZCML parsing.  Or just document that
  the registry can be mutated via the run.py code.

- Make ZCML filename argument optional to ``make_app``.  Document
  configuration without ZCML.

- Replace martian with something simpler.

- Maybe move code from within repoze.bfg.configuration.make_registry
  to repoze.bfg.registry.Registry constructor.