made number_to_words call everything else
refactor thousands, millions etc. into a split_into_triplets
extension into trillions - halfdone
fix bug: 'and' wasn't appearing when it should have been in numbers
>1000 with no hundreds column
Merge branch 'master' into infinity

Conflicts:
	numbers_to_words/number_to_words.rb
	numbers_to_words/spec/number_to_words_spec.rb
works for up to 999 trillion