Merge pull request #2 from johnnyshields/master

Replace String#ascii_zen_to_han with String#normalize_zen_han, which uses the existing Moji method.
Bump to 0.2.1
Correction to romaji_tables.rb:
1) Both シ and し should convert to 'shi'  (currently "し"=>"shi" and "シ"=>"si")
2) Add 2-char form of ツ which is 'tu'