Add some options to process_text

- min_words_to_check: minimum words to check before
  return a fiable result
- steps_before_check: check result every x steps
- confiable_ratio: confiable ratio between first and second result
- min_difference_words: minimum difference between first and second
  result
- min_word_length: minimum word size. Words smaller than than this value
  will be skipped