Training:

- Removed a lot of surface (SerializedFileReader ownership is really
  painful).
- Moved example + vision to hf.co version.
- Removed feature gate.

candle-examples/examples/mnist-training/main.rs

@@ -143,7 +143,7 @@ struct Args {
 pub fn main() -> anyhow::Result<()> {
     let args = Args::parse();
     // Load the dataset
-    let m = candle_datasets::vision::mnist::load_dir("data")?;
+    let m = candle_datasets::vision::mnist::load()?;
     println!("train-images: {:?}", m.train_images.shape());
     println!("train-labels: {:?}", m.train_labels.shape());
     println!("test-images: {:?}", m.test_images.shape());