def sets(opts = {}, &block)
      arry = client.list_sets.full.to_a
      return arry unless block_given?
      arry.map(&block)
    end
def sets(opts = {}, &block)
      arry = client.list_sets.full.to_a
      return arry unless block_given?
      arry.map(&block)
    end
Lists the sets available from the OAI endpoint. Accepts a block to
 pass to `#map` on the resulting array.

 @example:

   sets(&:spec)

 @param opts [Hash] options to pass to the OAI client
 @return [Array<OAI::Set>] an array of sets.

 @see OAI::Set