Create normalize method

* Makes text downcase without punctuation
Add remove_duplicate_words method

* Takes in sample text
* Calls normalize and converts string to array
* Removes duplicate words in the array
Create a word count function

* And rename remove_duplicate_words to unique_words
Add individual_word_counts method

* Creates a hash of all the words in a text as keys
* And their word counts as values
Create most_common_word method

* Returns the most common word over a certain minimum length from text
Add longest_words method and fix others

* Returns an array of the longest words
* Fix normalize to return array
* Fix individual word_counts to take an array for normalize
Change test case to Alice first chapter