This server script schedules the switching on or off of smart
   devices, such as, for example, the wifi of an at&t u-verse
   router connected to the local area network, depending on tcp
   messages received over port 29998 consisting of commands issued
   to do so via cron scheduling, or via telnet from an opened
   terminal, or from the send_to_smart_device_svr.lua client.
   Recognized commands include: 
      0
  1
  turn off wifi
  in 30 minutes turn wifi on for 2 hours and 30 minutes
  on 2009-11-05 disable wifi for 30 minutes at 3:00 pm
  on mon,tue,wed turn on wifi for 5 hours at 3:00pm
  mon - fri turn on wifi 3pm
      turn on wifi every day except thu from 3 to 5pm
  status wifi
      temp
  at midnight on fridays reboot wifi
  ... and variations on these themes.

 When using telnet, the user is only allowed 30 seconds to type
   in a command.  In the case of a two part non-recurring on and
   off command, if there exists conflicting events in crontab
   which prevent the command from uninterrupted fulfillment, then
   those events are commented out in the crontab, effectively
   placed on hold until the given command can run its course,
   after which time they are unheld.

 Additionally, at bootup, when the program is started, it
   assumes that the computer was offline during the last scheduled
   cron statement relating to turning on or off the device(s), and
   so, looks at the current users cron table and executes the last
   cron statement that happens to involve said device(s).

      Compiling of ccronexpr.so and ccronexpr_misc_utils.so may be accomplished by using the command `make all', executed from the root directory of the unzipped archive.

      ccronexpr.so is ordinarily compiled using the following statement:
         gcc -o ccronexpr.so ccronexpr.c -shared -fPIC -DCRON_USE_LOCAL_TIME

      ccronexpr_misc_utils.so is compiled by the following:
         gcc -o ccronexpr_misc_utils.so ccronexpr_misc_utils.c -shared -fPIC

      luajit and luasocket must be compiled, in their respective directories, using the command: make && make install
  For arm64, you'll need to instead delete the enclosed luaJit folder and download the latest luajit source using the command: git clone http://github.com/luajit/luajit.git
  (LuaJIT is not dead!  Mike Pall is evidently still very much kicking ass!)

      luasocket must have, in its src directory, a copy of lua.h luaconf.h and luaxlib.h, pertaining to lua-5.1, which have already been provided.

      The following scripts are copied to /usr/bin:
         send_to_smart_device_svr.lua  
         start_smart_device_svr.sh

      This is the crontab I've been using ( set with crontab -e, notice that there are no seconds fields ):

        59 22 * * sun,mon,tue,wed,thu screen -dm emacs -nw -Q -l /home/pi/code/smart_device_svr/disable_wifi.el
        0 15 * * mon,tue,wed,thu,fri screen -dm emacs -nw -Q -l /home/pi/code/smart_device_svr/enable_wifi.el
        59 23 * * fri,sat screen -dm emacs -nw -Q -l /home/pi/code/smart_device_svr/disable_wifi.el
        0 7 * * sat,sun screen -dm emacs -nw -Q -l /home/pi/code/smart_device_svr/enable_wifi.el

      ccronexpr.c is from https://github.com/staticlibs/ccronexpr

      The lua wrapper to ccronexpr.c is from
      https://github.com/tarantool/cron-parser/blob/master/cron-parser.lua but is not currently used

      table.save-1.0.lua is from http://lua-users.org/wiki/SaveTableToFile but is not currently used

      md5.lua is from https://github.com/kikito/md5.lua/blob/master/md5.lua

      LuaJIT-2.0.5 is from http://luajit.org/download.html