Serialized values for indexed columns and drying up the serializing part a little too

bagman.diff

diff --git a/lib/bagman/bag.rb b/lib/bagman/bag.rb
index df32a92..cb6ee30 100644
--- a/lib/bagman/bag.rb
+++ b/lib/bagman/bag.rb
@@ -51,17 +51,13 @@ module Bagman
       end
 
       target_class.send :define_method, "#{name}=" do |value|
+        serialised_value = self.class.serialise_value(value, options)
+
         if index_name = column.index_name
-          write_attribute(index_name, value)
+          write_attribute(index_name, serialised_value)
         end
 
-        self.bag[name] = if s = options[:serialize]
-                           s[value]
-                         elsif value.is_a? Date
-                           value.to_s(:db)
-                         else
-                           value.to_s
-                         end
+        self.bag[name] = serialised_value
       end
     end