doc add token filters

I've document the following.

http://createfield.com/groonga/en/reference/commands/table_create.html#token-filters
http://createfield.com/groonga/ja/reference/commands/table_create.html#token-filters

http://createfield.com/groonga/en/reference/token_filters.html
http://createfield.com/groonga/ja/reference/token_filters.html