(comment-start, comment-start-skip, comment-end): Made `defvar'.

(comment-start, comment-start-skip, comment-end): Made `defvar'.
(comment-style): Extract the choice out of comment-styles.
(comment-continue): Just a simple string now.
(comment-normalize-vars): Update for the new comment-continue.
(until, comment-end-quote-re): Removed.
(comment-quote-re, comment-quote-nested): New functions for quoting.
  These quote both the end and the start and also work for single-chars.
(comment-padright): Added lots of comments.
(comment-padleft): Added more comments.  Check comment-end rather than
  STR to determine whether N can be applied or not.
(uncomment-region): Rename BLOCK to BOX.
  Use the new comment-quote-nested.
  Use only one marker and properly set it back to nil.
  Be more picky when eliminating continuation markers.