Docker registry with external index is never standalone

As a registry with an external index it should not be considered standalone. Docker defaults to standalone is the header is not returned. This fixes a problem with running the registry and index over SSL.
Merge pull request #8 from AKoetsier/patch-1

Docker registry with external index is never standalone
webhook support and new variables for controlling the index
Merge branch 'master' of github.com:ekristen/docker-index

* 'master' of github.com:ekristen/docker-index:
  Docker registry with external index is never standalone
updating readme, adding properly working fig.yml file, updating version
updating README.md, actually poll the registry for docker headers
fixing ping function, which during tests was not returning properly
Update README.md
Update README.config.md