Add #queue and #next for Schedule

lib/crono/schedule.rb

@@ -5,6 +5,16 @@ module Crono
     end
 
     def add(peformer, period)
+      @schedule << [peformer, period]
+    end
+
+    def next
+      [queue.first[0], queue.first[1].next]
+    end
+
+    private
+    def queue
+      @schedule.sort { |a,b| a[1].next <=> b[1].next }
     end
   end
 end