'Implements Step 5a from "An algorithm for suffix stripping"
From the paper:
Step 5b
(m > 1 and *d and *L) -> single letter
controll       ->  control
roll           ->  roll'

def _step5b(self, word):

    return self._apply_rule_list(word, [(u'll', u'l', (lambda stem: (self._measure(word[:(-1)]) > 1)))])
