code: public Mutations<S> getRange(int from, int to) {
          return new Mutations<>(alphabet, Arrays.copyOfRange(mutations, from, to));
      }
docs: Extracts sub mutations by {@code from}-{@code to} mutation indices.
  
  @param from index in current mutations object pointing to the first mutation to be extracted
  @param to   index in current mutations object pointing to the next after last mutation to be extracted
  @return sub mutations