Write parser log file

Fix bug of skipping rule set IDs.
Remove unneeded out_sets from ItemSet class.

lib/propane/util.rb

@@ -0,0 +1,17 @@
+class Propane
+
+  # Utility methods.
+  module Util
+
+    class << self
+
+      def banner(message)
+        s = "*" * (message.size + 4)
+        "#{s}\n* #{message} *\n#{s}\n"
+      end
+
+    end
+
+  end
+
+end