Add logfile option

lib/crono/config.rb

@@ -1,14 +1,17 @@
 module Crono
   class Config
-    CRONOTAB = "config/cronotab.rb"
     include Singleton
+    CRONOTAB  = "config/cronotab.rb"
+    LOGFILE   = "log/crono.rb"
 
     attr_accessor :schedule
     attr_accessor :cronotab
+    attr_accessor :logfile
 
     def initialize
       self.schedule = Schedule.new
       self.cronotab = CRONOTAB
+      self.logfile  = LOGFILE
     end
   end