Added a very simple way of caching that cuts lag by 10x

The following results before this commit from Ruby's Benchmark:

        FrostyMeadow.generate x 50,000 #=> 5.2 seconds

This is mainly because the words are being read and parsed from words.json every single time. By implementing a cache, the time was cut by ~10x:

	FrostyMeadow.generate x 50,000 #=> 0.53 seconds