docs: function includeReferences(include, doc) {
    _.each(include, function (keypath) {
      var parts = keypath.split('.')
      var key = parts.shift()
  
      if (_.has(doc, key) && _.isString(doc[key])) {
        var ref = doc[key].split(':')
        doc[key] = getDocument({ collection: ref[0], id: ref[1] })
  
        if (parts.length > 0) {
          includeReferences(parts.slice(1), doc[key])
        }
      }
    })
  }