Add charge set/get callbacks (#600)

sfence

2022-06-06 0211c582e9ce8745e19ff49496b026d393dad074

 technic/machines/power_monitor.lua

@@ -55,7 +55,7 @@
         local demand = sw_meta:get_int("demand")
         meta:set_string("infotext",
               S("Power Monitor. Supply: @1 Demand: @2",
               technic.pretty_num(supply), technic.pretty_num(demand)))
               technic.EU_string(supply), technic.EU_string(demand)))
      else
         meta:set_string("infotext",S("Power Monitor Has No Network"))
      end