* calendar/todos.el: Comment out time-stamp require; require

* calendar/todos.el: Comment out time-stamp require; require
calendar and diary-lib.
(todos-prefix): Change default value and doc string to reflect new
meaning; add :initialize and :set functions.
(todos-time-string-format, todos-entry-prefix-function)
(todos-initials, todos-entry-timestamp-initials)
(todos-prefix-face, todos-category-sep, todos-category-end)
(todos-cp): Comment out.
(todos-prefix-string): Inherit from font-lock-comment-face.
(todos-item-header, todos-item-header-face): Remove.
(todos-date, todos-time): New faces.
(todos-date-face, todos-time-face): Corresponding new variables.
(todos-add-time-string, todos-include-in-diary)
(todos-exclusion-start, todos-exclusion-end, todos-number-prefix):
New defcustoms.
(todos-item-end, todos-item-start-overlays)
(todos-item-end-overlays): New variables.
(todos-date-string-match, todos-time-string-match): New functions.
(todos-font-lock-keywords): Use them.
(todos-current-date, todos-date-string, todos-time-string)
(todos-toggle-item-diary-inclusion, todos-toggle-diary-inclusion)
(todos-reset-prefix, todos-update-numbered-prefix)
(todos-check-overlay, todos-item-overlays)
(todos-insert-with-overlays, todos-show-paren-hack): New functions.
(todos-highlight-item): New command.
(todos-category-beg): Change value.
(todos-category-select): Use todos-category-beg and todos-item-overlays.
(todos-backward-item): Add optional count argument; use it and
todos-item-start.
(todos-forward-item): Use todos-check-overlay, todos-item-start
and variable todos-item-end.
(todos-edit-item, todos-delete-item): Use todos-number-prefix,
todos-update-numbered-prefix, todos-item-overlays.
(todos-add-category, todos-rename-category)
(todos-list-categories): Use new category format.
(todos-delete-category): Allow deleting non-empty category;
use new category format.
(todos-add-item-non-interactively): Comment out unnecessary
save-excursion; use todos-insert-with-overlays.
(todos-insert-item): Comment out unnecessary save-excursion; use
new item format for date/time header and diary inclusion marking.
(todos-insert-item-here): Use new item format for date/time header
and diary inclusion marking; use todos-insert-with-overlays.
(todos-raise-item): Make a no-op if point is on an empty line; use
todos-insert-with-overlays.
(todos-lower-item): Use todos-insert-with-overlays.
(todos-top-priorities): Move call to todos-show inside
save-excursion; add save-current-buffer after save-restriction.
(todos-item-start): Use variable todos-item-end.
(todos-item-end): Use todos-check-overlay and variable todos-item-end.
(todos-remove-item): Take item overlays into account.
(todos-mode): Change calculation of wrap-prefix; make
hl-line-range-function a local variable and set it to highlight
todo item.
(todos-show): Ensure point stays at top of category.