add support for pathlib to load and dump (#91)

* add support for pathlib to load and dump

* minor formatting

mmcv/fileio/io.py

+from pathlib import Path
+
 from ..utils import is_list_of, is_str
 from .handlers import BaseFileHandler, JsonHandler, PickleHandler, YamlHandler
 
@@ -16,7 +18,8 @@ def load(file, file_format=None, **kwargs):
     This method provides a unified api for loading data from serialized files.
 
     Args:
-        file (str or file-like object): Filename or a file-like object.
+        file (str or :obj:`Path` or file-like object): Filename or a file-like
+            object.
         file_format (str, optional): If not specified, the file format will be
             inferred from the file extension, otherwise use the specified one.
             Currently supported formats include "json", "yaml/yml" and
@@ -25,6 +28,8 @@ def load(file, file_format=None, **kwargs):
     Returns:
         The content from the file.
     """
+    if isinstance(file, Path):
+        file = str(file)
     if file_format is None and is_str(file):
         file_format = file.split('.')[-1]
     if file_format not in file_handlers:
@@ -48,14 +53,16 @@ def dump(obj, file=None, file_format=None, **kwargs):
 
     Args:
         obj (any): The python object to be dumped.
-        file (str or file-like object, optional): If not specified, then the
-            object is dump to a str, otherwise to a file specified by the
-            filename or file-like object.
+        file (str or :obj:`Path` or file-like object, optional): If not
+            specified, then the object is dump to a str, otherwise to a file
+            specified by the filename or file-like object.
         file_format (str, optional): Same as :func:`load`.
 
     Returns:
         bool: True for success, False otherwise.
     """
+    if isinstance(file, Path):
+        file = str(file)
     if file_format is None:
         if is_str(file):
             file_format = file.split('.')[-1]