Rename a new cal-tex function, document it

Rename a new cal-tex function, document it

* lisp/calendar/cal-tex.el (cal-tex-diary, cal-tex-cursor-week)
(cal-tex-cursor-week2, cal-tex-cursor-week-iso)
(cal-tex-cursor-week-monday): Doc fixes.
(cal-tex-cursor-week2-summary): Doc fix.
Rename from cal-tex-cursor-week-at-a-glance.

* lisp/calendar/calendar.el (calendar-mode-map):
Add cal-tex-cursor-week2-summary.

* lisp/calendar/cal-menu.el (cal-menu-context-mouse-menu):
Tweak week descriptions.  Add cal-tex-cursor-week2-summary.

* doc/emacs/calendar.texi (Writing Calendar Files): Tweak week descriptions.
Mention cal-tex-cursor-week2-summary.