* calendar/todos.el: Numerous spelling and comment fixes, doc

* calendar/todos.el: Numerous spelling and comment fixes, doc
string fixes to conform with checkdoc, further rearrangement of
definitions, etc.
(todos-previous-line, todos-previous-answer)
(todos-insert-item-ask-date, todos-change-date)
(todos-date-nodayname-pattern, todos-dayname-date-pattern)
(todos-count-items-in-category, todos-count-all-items): Remove.
(todos-update-numbered-prefix, todos-item-start-overlays)
(todos-add-item-non-interactively): Comment out, also in uses.
(todos-done-separator): Change default value.
(todos-always-add-time-string): Rename from todos-add-time-string
and adjust uses.
(todos-read-category): Rename from todos-completing-read and
adjust callers; use todos-current-category.
(todos-make-categories-alist): Rename from function
todos-categories-alist.
(todos-categories-alist): New variable.
(todos-indent-to-here): New defcustom.
(todos-button): New face.
(todos-display-categories-alphabetically, todos-raise-category)
(todos-lower-category, todos-insert-item-for-diary-ask-date-time)
(todos-insert-item-here-ask-date-time)
(todos-insert-item-ask-date-time)
(todos-insert-item-ask-dayname-time): New commands.
(todos-edit-item-header): New command replacing todos-change-date.
(todos-category-number, todos-indent, todos-item-counts)
(todos-check-category-name, todos-read-date, todos-read-dayname)
(todos-read-time, todos-padded-string)
(todos-insert-category-name): New functions.
(todos-set-item-priority): New function replacing
todos-add-item-non-interactively.
(todos-mode-map): Remap newline to newline-and-indent.
(todos-edit-mode-map): Make sparse keymap; remap newline to
newline-and-indent.
(todos-categories-mode-map): New keymap.
(todos-mode, todos-edit-mode): Make indent-line-function local
variable and set to todos-indent.
(todos-categories-mode): New major mode.
(todos-display-categories): List categories initially in their
numerical order; add optional argument to switch to alphabetical
listing.
(todos-toggle-view-done-items): Simplify implementation.
(todos-toggle-display-date-time): Fix regexp search string.
(todos-backward-item, todos-forward-item): Use variable
todos-item-start.
(todos-add-category): Use todos-check-category-name and
todos-categories-alist.
(todos-rename-category): Use todos-current-category,
todos-check-category-name and todos-categories-alist.
(todos-delete-category): Use todos-check-category-name and
todos-categories-alist and take done items into account.
(todos-insert-item): Use separate arguments to handle insertion of
date/dayname and time strings, add new argument to mark item for
diary inclusion, use new todos-read-* functions,
todos-set-item-priority and todos-item-counts.
(todos-insert-item-here, todos-insert-item-for-diary)
(todos-insert-item-from-calendar): Adapt to new version of
todos-insert-item.
(todos-delete-item, todos-item-done): Use todos-item-counts.
(todos-edit-item): Indent newlines inserted by C-q C-j if nonspace
char follows.
(todos-lower-item): Ensure only not-done items can be lowered.
(todos-move-item): Use todos-current-category, todos-read-category
and todos-item-counts.
(todos-archive-done-items): Use todos-current-category and
todos-item-counts; fix regexp search string.
(todos-item-undo): Use todos-current-category,
todos-set-item-priority, todos-insert-with-overlays and
todos-item-counts; restore if user quits before inserting undone
item.
(todos-date-pattern): Rewrite without using
todos-date-nodayname-pattern and todos-dayname-date-pattern.
(todos-date-string-match): Do not make todos-date-pattern an
unnumbered group.
(todos-time-string-match): Make todos-date-pattern a shy group.
(todos-wrap-and-indent): Use todos-indent-to-here.
(todos-reset-prefix): Revert to using todos-show instead of
todos-category-select.
(todos-prefix-overlays): Fix numbering of done items and updating
of prefix.
(todos-category-select): Use todos-current-category; fix display
of separator string; don't move point to top of category.
(todos-jump-to-category-noninteractively): Use todos-category-number.
(todos-insert-with-overlays): Use todos-item-start unconditionally.
(todos-item-start): New variable.
(todos-item-start): Use it to define this function.
(todos-item-end): Adjust if item is last unfinished one before
displayed done items.
(todos-remove-item): Use todos-item-start and todos-item-end
instead of todos-forward-item and todos-backward-item.
(todos-longest-category-name-length): Add argument for list of
categories.