'_break_word(word : string, space_left : int) -> (string, string)
Break line by unicode width instead of len(word).'

def _break_word(self, word, space_left):

    total = 0
    for (i, c) in enumerate(word):
        total += column_width(c)
        if (total > space_left):
            return (word[:(i - 1)], word[(i - 1):])
    return (word, '')
