Made it possible to call has_details multiple times on the same column

lib/has_details.rb

@@ -37,7 +37,10 @@ def has_details(options = {})
       raise(ArgumentError, "You must be supply at least one field in the configuration hash") unless configuration.keys.size > 0
 #      raise(Exception, "A #{configuration[:column]} column must be present in the database for this plugin.") unless columns.include?(:details)
 
-      serialize configuration.delete(:column), Hash
+      col = configuration.delete(:column).to_s
+      unless serialized_attributes[col]
+        serialize col, Hash
+      end
 
       configuration.each do |f,t|