Use overlays rather than selective-display.

Use overlays rather than selective-display.
(diary-selective-display): New var.
(diary-header-line-format): Use it.
(diary-list-entries): Add argument `list-only'.
Put the buffer in diary-mode.  Don't add \^M at beg and end.
Replace \^M by invisible overlays.
(diary-unhide-everything): Replace \^M by invisible overlays.
(print-diary-entries): Look for overlays rather than \^M.
Add a space to the temp buffer name.
(diary-show-all-entries, mark-diary-entries, make-diary-entry):
Put the buffer in diary-mode.
(list-sexp-diary-entries): Replace \^M by invisible overlays.
(diary-anniversary): Make the year arg optional.
(diary-time-regexp): New const.
(diary-font-lock-keywords): Use it to accept a few more time formats.