Make definition of both Kaminari and WillPaginate warnings occur only if user hasn't explicitly set one of the paginators

Author: eidge

lib/api-pagination/configuration.rb

@@ -13,7 +13,10 @@ def configure(&block)
     def initialize
       @total_header    = 'Total'
       @per_page_header = 'Per-Page'
-      set_paginator
+    end
+
+    def paginator
+      @paginator || set_paginator
     end
 
     def paginator=(paginator)
@@ -67,6 +70,8 @@ def set_paginator
 gem 'will_paginate'
 
 WARNING
+
+      @paginator
     end
 
     def use_kaminari