Top Words in a Review

You want to know which words a customer used most in a review.

Write top_words(text, n). It returns a list of the n most frequent words, most frequent first.

• Split the text on spaces and treat words as lowercase ("Good" and "good" are the same word).
• If two words are used the same number of times, the one that appeared earlier in the text comes first.
• If there are fewer than n different words, return all of them.
• Empty text gives back an empty list.