add Schedule class & add time.schedule.world schedule group

res/modules/schedule.lua

@@ -0,0 +1,37 @@
+local Schedule = {
+    __index = {
+        set_interval = function(self, ms, callback)
+            local id = self._next_interval
+            self._intervals[id] = {
+                last_called = 0.0,
+                delay = ms / 1000.0,
+                callback = callback,
+            }
+            self._next_interval = id + 1
+            return id
+        end,
+        tick = function(self, dt)
+            local timer = self._timer + dt
+            for id, interval in pairs(self._intervals) do
+                if timer - interval.last_called >= interval.delay then
+                    xpcall(interval.callback, function(s)
+                        debug.error(s..'\n'..debug.traceback())
+                    end)
+                    interval.last_called = timer
+                end
+            end
+            self._timer = timer
+        end,
+        remove_interval = function (self, id)
+           self._intervals[id] = nil
+        end
+    }
+}
+
+return function ()
+    return setmetatable({
+        _next_interval = 1,
+        _timer = 0.0,
+        _intervals = {},
+    }, Schedule)
+end