Two small fixes related to the checkpoint loader (#36)

- Checkpoint loader test: we do not need to download `config.json`
  anymore, since the loading is now in-place.
- Export checkpoint loader constructor from `models` module.

spacy_curated_transformers/models/__init__.py

@@ -6,6 +6,7 @@
     build_camembert_transformer_model_v1,
     build_camembert_transformer_model_v2,
     build_pytorch_checkpoint_loader_v1,
+    build_pytorch_checkpoint_loader_v2,
     build_roberta_transformer_model_v1,
     build_roberta_transformer_model_v2,
     build_xlmr_transformer_model_v1,

spacy_curated_transformers/tests/models/test_transformer_model.py

@@ -169,7 +169,6 @@ def test_pytorch_checkpoint_loader(test_config):
 
     checkpoint_path = hf_hub_download(repo_id=model_name, filename="pytorch_model.bin")
     # Curated Transformers needs the config to get the model hyperparameters.
-    hf_hub_download(repo_id=model_name, filename="config.json")
     with_spans = build_with_strided_spans_v1(stride=96, window=128)
     model = model_factory(
         piece_encoder=piece_encoder, vocab_size=vocab_size, with_spans=with_spans