add timer class for periodic runs

lib/timer/GwTimer.h

@@ -0,0 +1,48 @@
+#ifndef _GWTIMER_H
+#define _GWTIMER_H
+#include <vector>
+#include <functional>
+#include <Arduino.h>
+class GwIntervalRunner{
+    public:
+    using RunFunction=std::function<void(void)>;
+    private:
+    class Run{
+        public:
+        unsigned long interval=0;
+        RunFunction runner;
+        unsigned long last=0;
+        Run(RunFunction r,unsigned long iv,unsigned long l=0):
+            runner(r),interval(iv),last(l){}
+        bool shouldRun(unsigned long now){
+            if ((last+interval) > now) return false;
+            last=now;
+            return true;
+        }
+        bool runIf(unsigned long now){
+            if (shouldRun(now)) {
+                runner();
+                return true;
+            }
+            return false;
+        }
+    };
+    std::vector<Run> runners;
+    unsigned long startTime=0;
+    public:
+    GwIntervalRunner(unsigned long now=millis()){
+        startTime=now;
+    }
+    void addAction(unsigned long interval,RunFunction run,unsigned long start=0){
+        if (start=0) start=startTime;
+        runners.push_back(Run(run,interval,start));
+    }
+    bool loop(unsigned long now=millis()){
+        bool rt=false;
+        for (auto it=runners.begin();it!=runners.end();it++){
+            if (it->runIf(now)) rt=true;
+        }
+        return rt;
+    }
+};
+#endif