Exceptions for "kannji" and "kannzi"

[blagarde]

Test cases for the following functions currently check the output of "kannji" and "kannzi":

to_katakana(...) - Convert a Romaji (ローマ字) to a Katakana (片仮名).
to_kana(...) - Convert a Romaji (ローマ字) to a Katakana (片仮名). (same as to_katakana)
to_hiragana(...) - Convert a Romaji (ローマ字) to a Hiragana (平仮名).
to_hepburn(...) - Convert a Kana (仮名) or a Kunrei-shiki Romaji (訓令式ローマ字) to a Hepburn Romaji (ヘボン式ローマ字).

These two forms ("kannji" and "kannzi"), are valid in neither Hepburn nor Kunrei romanization schemes therefore they cannot be considered valid "Romaji" input. when When given these inputs, instead of returning values ("カンジ", "かんじ", and "kanji"), the four above functions should raise an exception.

If we wanted to preserve the ability to convert from these forms, support for a third form of romanization should be added - "Wāpuro rōmaji" (word processor romaji):
http://en.wikipedia.org/wiki/W%C4%81puro_r%C5%8Dmaji