Address #1551 - better timers handling

src/timer.h

@@ -7,15 +7,14 @@ struct mg_timer {
   uint64_t prev_ms;         // Timestamp of a previous poll
   uint64_t expire;          // Expiration timestamp in milliseconds
   unsigned flags;           // Possible flags values below
-#define MG_TIMER_REPEAT 1   // Call function periodically, otherwise run once
+#define MG_TIMER_ONCE 0     // Call function once
+#define MG_TIMER_REPEAT 1   // Call function periodically
 #define MG_TIMER_RUN_NOW 2  // Call immediately when timer is set
   void (*fn)(void *);       // Function to call
   void *arg;                // Function argument
-  struct mg_timer *next;    // Linkage in g_timers list
+  struct mg_timer *next;    // Linkage
 };
 
-extern struct mg_timer *g_timers;  // Global list of timers
-
 void mg_timer_init(struct mg_timer **head, struct mg_timer *timer,
                    uint64_t milliseconds, unsigned flags, void (*fn)(void *),
                    void *arg);