text: Title: Tokenization in 8.2.2
  Body: I think in tokenize function, if it's tokenizing words, it should add space_character to tokens too. Otherwise, in predict function, it will assume '<unk>' for spaces and the predictions doesn't have spaces between them (which can be solved by manipulating the predict function to this line: `return ''.join([vocab.idx_to_token[i] + ' ' for i in outputs])`)
  
  I think tokenized should change like this:
  
  `[line.split() for line in lines] + [[' ']]`
  
  If I'm right, I can make a pr for both tokenize and predict funcs. (although for predict I might have to change inputs of function as well to recognize if it's a char level or word lever rnn)