'Returns True if word[i] is a consonant, False otherwise
A consonant is defined in the paper as follows:
A consonant in a word is a letter other than A, E, I, O or
U, and other than Y preceded by a consonant. (The fact that
the term `consonant\' is defined to some extent in terms of
itself does not make it ambiguous.) So in TOY the consonants
are T and Y, and in SYZYGY they are S, Z and G. If a letter
is not a consonant it is a vowel.'

def _is_consonant(self, word, i):

    if (word[i] in self.vowels):
        return False
    if (word[i] == u'y'):
        if (i == 0):
            return True
        else:
            return (not self._is_consonant(word, (i - 1)))
    return True
