use nonblocking write for serial

lib/log/GwLog.h

@@ -1,17 +1,25 @@
 #ifndef _GWLOG_H
 #define _GWLOG_H
 #include <Arduino.h>
+
+class GwLogWriter{
+    public:
+        virtual ~GwLogWriter(){}
+        virtual void write(const char *data)=0;
+};
 class GwLog{
     private:
         char buffer[100];
-        bool logSerial=false;
         int logLevel=1;
+        GwLogWriter *writer;
     public:
         static const int LOG=1;
         static const int ERROR=0;
         static const int DEBUG=3;
         static const int TRACE=2;
-        GwLog(bool logSerial,int level=LOG);
+        String prefix="LOG:";
+        GwLog(int level=LOG, GwLogWriter *writer=NULL);
+        void setWriter(GwLogWriter *writer);
         void logString(const char *fmt,...);
         void logDebug(int level, const char *fmt,...);
         int isActive(int level){return level <= logLevel;};