Implemented function to list data files

Update function to list data files

Follow Style Guidelines

Add doc for listing files

interfaces/cython/cantera/data/__init__.py

@@ -0,0 +1,15 @@
+from pathlib import Path
+
+
+def list_data_files(ext=''):
+    """
+    Lists input data files.
+
+    :param ext:
+        Extension of files to be displayed.
+    :return:
+        List of input data files.
+    """
+    here = Path(__file__).parent
+    data_files = [x.name for x in here.iterdir() if not x.name.startswith('__') and x.name.endswith(ext)]
+    return data_files