cron: use Lua table rather than native array
cron: use Lua table rather than native array

Pin a table to the registry and use that instead of manually allocating
and reallocating and shuffling integers around.

Thanks to @TerryE for some style suggestions.

nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware