Fix #1285 - __builtin___snprintf_chk warning. Tighten test flags and refactor the code to squash all warnings

src/timer.h

@@ -1,8 +1,8 @@
 #pragma once
 
 struct mg_timer {
-  int period_ms;            // Timer period in milliseconds
-  int flags;                // Possible flags values below
+  unsigned long period_ms;  // Timer period in milliseconds
+  unsigned flags;           // Possible flags values below
 #define MG_TIMER_REPEAT 1   // Call function periodically, otherwise run once
 #define MG_TIMER_RUN_NOW 2  // Call immediately when timer is set
   void (*fn)(void *);       // Function to call
@@ -13,6 +13,7 @@ struct mg_timer {
 
 extern struct mg_timer *g_timers;  // Global list of timers
 
-void mg_timer_init(struct mg_timer *, int ms, int, void (*fn)(void *), void *);
+void mg_timer_init(struct mg_timer *, unsigned long ms, unsigned,
+                   void (*fn)(void *), void *);
 void mg_timer_free(struct mg_timer *);
 void mg_timer_poll(unsigned long uptime_ms);