Update ExternalProjectDependency system based on commontk/Artichoke@c3eb170

$ git shortlog 70ed903..c3eb170
Jean-Christophe Fillion-Robin (5):
      Update README.md - Add 'Features', 'API' and 'Examples" section
      Include link to example of configure output to README file
      Fix typo preventing additional external project from being considered
      Ensure a list of same labels can be associated with multiple variables
      Simplify API removing requirement to explicitly set 'CMAKE_CMD' parameter