* lisp/calendar/timeclock.el: Use lexical-binding

* lisp/calendar/timeclock.el: Use lexical-binding

Require cl-lib.  Remove redundant :group args.
(timeclock-status-string): Avoid 'setq'.
(timeclock-ask-for-project, timeclock-ask-for-reason):
Completionu tables can be simple lists of strings.
(timeclock-read-moment): Doesn't deserve to be defsubst (most of the
others don't either, admittedly).
(timeclock-entry): New type.
(timeclock-entry-begin, timeclock-entry-end, timeclock-entry-project)
(timeclock-entry-comment): Define via 'cl-defstruct'.
(timeclock-entry-list-projects, timeclock-day-list-projects):
Avoid add-to-list on lexical vars.
(timeclock-day-list): Use 'push'.
(timeclock-log-data): Use 'pcase'.
(timeclock-mean): Simplify.
(timeclock-generate-report): Use dotimes.