Use int64_t for timers and mg_millis()

src/event.h

@@ -9,7 +9,7 @@ void mg_error(struct mg_connection *c, const char *fmt, ...);
 enum {
   MG_EV_ERROR,       // Error                        char *error_message
   MG_EV_OPEN,        // Connection created           NULL
-  MG_EV_POLL,        // mg_mgr_poll iteration        unsigned long *millis
+  MG_EV_POLL,        // mg_mgr_poll iteration        int64_t *milliseconds
   MG_EV_RESOLVE,     // Host name is resolved        NULL
   MG_EV_CONNECT,     // Connection established       NULL
   MG_EV_ACCEPT,      // Connection accepted          NULL
@@ -24,6 +24,6 @@ enum {
   MG_EV_MQTT_CMD,    // MQTT low-level command       struct mg_mqtt_message *
   MG_EV_MQTT_MSG,    // MQTT PUBLISH received        struct mg_mqtt_message *
   MG_EV_MQTT_OPEN,   // MQTT CONNACK received        int *connack_status_code
-  MG_EV_SNTP_TIME,   // SNTP time received           struct timeval *
+  MG_EV_SNTP_TIME,   // SNTP time received           int64_t *milliseconds
   MG_EV_USER,        // Starting ID for user events
 };