Two words are anagrams if the letters of one can be rearranged to form the other. For example, mar, ram, and arm are all anagrams of each other. One way to quickly identify whether two arbitrary words are anagrams are to sort the letters in each word to produce a signature. (The above words all have the signature 'amr'.) Two words are anagrams if and only if they have the same signature. Write a function called anagrams() that takes the name of a text file as its only parameter. The file is assumed to have one word per line, all lower-case. The function returns a dictionary in which the keys are signatures of words in the file and the value for each key is the set of all words in the file having that particular signature.