disk_usage() on windows + python 3 should be able to accept bytes

[giampaolo]

>>> import psutil
>>> psutil.disk_usage('.')
sdiskusage(total=42423283712, used=31134781440, free=11288502272, percent=73.4)
>>> psutil.disk_usage(b'.')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\user\Desktop\psutil\psutil\__init__.py", line 2020, in disk_usage
    return _psplatform.disk_usage(path)
  File "C:\Users\user\Desktop\psutil\psutil\_pswindows.py", line 247, in disk_usage
    total, free = cext.disk_usage(path)
TypeError: argument 1 must be str, not bytes
>>>

All os.* and fs-related functions on Python 3 are able to so also should psutil.