Add fs arg to mg_file* and mg_http_upload API

examples/complete/main.c

@@ -147,7 +147,7 @@ static void broadcast_mjpeg_frame(struct mg_mgr *mgr) {
   static size_t i;
   const char *path = files[i++ % nfiles];
   size_t size = 0;
-  char *data = mg_file_read(path, &size);  // Read next file
+  char *data = mg_file_read(&mg_fs_posix, path, &size);  // Read next file
   struct mg_connection *c;
   for (c = mgr->conns; c != NULL; c = c->next) {
     if (c->label[0] != 'S') continue;         // Skip non-stream connections

examples/esp32/main/main.c

@@ -40,7 +40,7 @@ void app_main(void) {
       .base_path = FS_ROOT, .max_files = 20, .format_if_mount_failed = true};
   int res = esp_vfs_spiffs_register(&conf);
   LOG(res == ESP_OK ? LL_INFO : LL_ERROR, ("FS %s, %d", conf.base_path, res));
-  mg_file_printf(FS_ROOT "/hello.txt", "%s", "hello from ESP");
+  mg_file_printf(&mg_fs_posix, FS_ROOT "/hello.txt", "%s", "hello from ESP");
 
   // Setup wifi. This function is implemented in wifi.c
   // It blocks until connected to the configured WiFi network

examples/video-stream/main.c

@@ -33,7 +33,7 @@ static void broadcast_mjpeg_frame(struct mg_mgr *mgr) {
   static size_t i;
   const char *path = files[i++ % nfiles];
   size_t size = 0;
-  char *data = mg_file_read(path, &size);  // Read next file
+  char *data = mg_file_read(&mg_fs_posix, path, &size);  // Read next file
   struct mg_connection *c;
   for (c = mgr->conns; c != NULL; c = c->next) {
     if (c->label[0] != 'S') continue;         // Skip non-stream connections