change README-ja.rdoc encoding to utf-8
ver 0.1.10
add field_group to missing if required
raise execption if filter method is not defined
ver. 0.1.11
add magick comment
fix filter to support ruby1.9 (Array#to_s output is changed)
dont change hash duaring iteration (support ruby 1.9)
use "blank?" instead of "to_s.empty?"

ruby 1.8

  nil.to_s => ""
  [].to_s  => ""
  "".to_s  => ""

ruby 1.9

   nil.to_s => ""
   [].to_s  => "[]"
   "".to_s  => ""
ver. 1.12 Ruby 1.9 Support
swap left and right (class name must be left)
if result_symbol is true invalid keys to be symbole