Read all the files and tokenize their text into words and
        accumulate all the words in a list.

def start_indexing(self):
        """
        Read all the files and tokenize their text into words and
        accumulate all the words in a list.
        """
        for filepath in self.filepaths:
            with open(filepath) as fp:
                blob = fp.read()
                self.words.extend(self.tokenize(blob))