add BIDSFile subclasses to namespace

Author: tyarkoni

bids/layout/__init__.py

@@ -1,7 +1,15 @@
 from .layout import BIDSLayout, add_config_paths, parse_file_entities
-from .models import BIDSFile
+from .models import BIDSFile, BIDSImageFile, BIDSDataFile, BIDSJSONFile
 # Backwards compatibility
 from bids_validator import BIDSValidator
 
-__all__ = ["BIDSLayout", "BIDSValidator", "add_config_paths",
-           "parse_file_entities", "BIDSFile"]
+__all__ = [
+    "BIDSLayout",
+    "BIDSValidator",
+    "add_config_paths",
+    "parse_file_entities",
+    "BIDSFile",
+    "BIDSImageFIle",
+    "BIDSDataFile",
+    "BIDSJSONFile",
+]