English: pluralize 'vowel+o' ending as 'vowel+o+s'

See:
* The Cambridge Grammar of the English Language (p. 1586, The alternation between ·s and ·es)
* http://english.stackexchange.com/questions/23229/is-there-a-good-rule-of-thumb-for-plurals-from-words-ending-in-o
* http://www.oxforddictionaries.com/us/words/plurals-of-nouns