code: function followPageRecursively( pageRef ) {
           return followPage( pageRef )
              .then( pages => Promise.all(
                 [ Promise.resolve( pages ) ].concat( pages.map( followPageToPages ) )
              ) )
              .then( flatten );
        }
docs: ///////////////////////////////////////////////////////////////////////////////////////////////////// 
  Collect meta information about the given page, and about all pages reachable from it, recursively.
  Skip collection if the page has already been processed (returning an empty result array).
  
  @private
  @param {String} pageRef the page reference (relative to `paths.pages`) to follow
  @return {Promise<Array>}
  a promise for an array of page-meta objects for this page, including the page itself