* calendar/todos.el: Further comment revision.

* calendar/todos.el: Further comment revision.
(todos-set-item-top-priority): New command.
(todos-reset-global-current-todos-file):
Use todos-files-function instead of todos-files.
(todos-read-category): Add optional argument to test whether
caller adds new category; if so, don't prompt for new category and
don't restore original todos-categories list.
(todos-categories-mode-map): Update to renamed commands.
(todos-filter-items-mode-map): Add binding for new command.
(todos-mode): Fix typo.
(todos-show): If called from archive file, show corresponding
category in Todos file, if it exists.
(todos-jump-to-category): Remove code to add new category, since
todos-read-category can do that.
(todos-add-file): Remove obsolete code; visit new file in selected
window.
(todos-add-category): Simplify.
(todos-rename-category): Use force-mode-line-update instead of
setting mode-line-buffer-identification.
(todos-delete-category): Improve logic of prompts; use
todos-categories-full and check todos-ignore-archived-categories.
(todos-raise-category-priority, todos-lower-category-priority):
Rename from todos-{raise,lower}-category and adjust callers.
(todos-move-category, todos-merge-category):
Set todos-categories-full; on setting todos-categories check
todos-ignore-archived-categories.
(todos-insert-item): Let-bind use-empty-active-region and use
use-region-p instead of transient-mark-mode.
(todos-raise-item-priority): Improve implementation.
(todos-archive-done-item): Rename from
todos-archive-done-item-or-items and adjust callers; confine to
Todos mode.
(todos-unarchive-items): On setting todos-categories check
todos-ignore-archived-categories.