def collections
      @collections ||= Hash[collection_names.map do |coll|
        [coll, Bunto::Collection.new(self, coll)]
      end]
    end
def collections
      @collections ||= Hash[collection_names.map do |coll|
        [coll, Bunto::Collection.new(self, coll)]
      end]
    end
The list of collections and their corresponding Bunto::Collection instances.
 If config['collections'] is set, a new instance is created
 for each item in the collection, a new hash is returned otherwise.

 Returns a Hash containing collection name-to-instance pairs.