Log message:
Update to 1.6.0:

v1.6.0
======

* bail out early if the scm is missing

  this brings issues with git tarballs and
  older devpi-client releases to light,
  before we would let the setup stay at version 0.0,
  now there is a ValueError

* propperly raise errors on write_to missuse (thanks Te-jé Rodgers)

Log message:
Import py34-setuptools_scm-1.5.5 as devel/py-setuptools_scm.

setuptools_scm handles managing your python package versions in
scm metadata. It also handles file finders for the supperted scms.