* calendar/todos.el (todos-reset-done-separator-string):
Complete the implementation.
(todos-hide-show-done-items): If start of done items sections is
below the bottom of the window, make it visible.
(todos-insert-item): Allow inserting item here to work outside of
the current category, but then at top of category. After checking
whether only done items are shown, restore point to ensure
inserting item here works correctly.
(todos-set-item-priority): Delete leftover right paren at end.