Rework parameters for picoLisp timer module.

* tmr-delay will now accept the time period
  parameter and an optional timer id (both
  parameters are numbers). If id is not
  specified, sys-timer is selected.

* tmr-read will now accept an optional timer
  id (parameter type is num). Passing no
  parameter will force the funtion to assume
  sys-timer for timer id.
Internal picoLisp symbol: *sys-timer*

* Support code for including *sys-timer*
  as an internal (protected) picoLisp
  symbol.

* Add helper macro 'plen' which returns
  the number of parameters passed to a
  function.

* Include simplemachines-italy in the
  copyright for picolisp/src/pico.h