kill the distiller.  build eggs using setuptools.  add wheel builder.

At a high level this review:
  1) Kills the distiller (the reasons we had it (recursive zipimporting) are no longer relevant)
  2) Uses setuptools directly to build eggs (and with a few extra lines of code extends this to
     build wheels.)
  3) Augments PythonInterpreter to be aware of 'capabilities' -- i.e. requirements that it can
     resolve
  4) Augments PythonInterpreterCache to be aware of capabilities

Wheels still can't be used -- that requires a full implementation of PEP425
tag matching, which is a subsequent review.

Testing Done:
build-support/bin/ci.sh

Reviewed at https://rbcommons.com/s/twitter/r/55/