/* You are given a set<string> containing all of the words in the English
 * language, all in lowercase.  Write a function that takes in a string prefix,
 * then prints out all of the words in the set that have that string as
 * a prefix.  However, if you iterate over an element of the set, you must
 * print it out (that is, you can't just iterate over the set and print out
 * words with the right prefixes.  You need to find a way to iterate over
 * just those words with the right prefix)
 */