Hi,

Why not have emacs to count sentences besides lines, words and
characters? So far, here is the patch that I end up with.

Comments:

    - the `count-sentences' function seems a bit out of place in
      "simple.el" but since I'm using it here I left it there;
          
    - I had to ignore-errors on (end-of-paragraph-text) in
      `forward-sentence' otherwise `count-words' won't work on a buffer
      without a terminal new line. But now `forward-sentence' won't
      error out at the end of buffer. Maybe there is a way around it
      that I don't know.