(timer): Define as a defstruct, so we can name the fields, to make the

(timer): Define as a defstruct, so we can name the fields, to make the
code clearer.  Rewrite all `aset' and `aref' using the defined accessors.
(timer--time): New pseudo-field.
(timer-set-time, timer-set-idle-time, timer-inc-time)
(timer-set-time-with-usecs, with-timeout-suspend): Use it.
(timer--time-less-p): New function.
(timer--activate): New function, extracted from timer-activate.
(timer-activate-when-idle, timer-activate): Use it.
(cancel-function-timers): Use dolist.