[bug]: mudkip develop issues error trace but keeps working

[epogrebnyak]

This is not a big pain, but takes few tries to get used to - on Windows mudkip develop starts with error message:

Watching "docs"...
Server running on http://localhost:5500
q:\chaos\docs\index.rst:4: WARNING: toctree contains reference to nonexisting document 'README'
q:\chaos\docs\link.md: WARNING: document isn't included in any toctree
Process Process-1:
Traceback (most recent call last):
  File "c:\users\epogr\anaconda3\lib\multiprocessing\process.py", line 315, in _bootstrap
    self.run()
  File "c:\users\epogr\anaconda3\lib\multiprocessing\process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "c:\users\epogr\anaconda3\lib\site-packages\mudkip\server.py", line 32, in serve_directory
    server.serve(port=port, host=host, root=directory)
  File "c:\users\epogr\anaconda3\lib\site-packages\livereload\server.py", line 339, in serve
    self.application(
  File "c:\users\epogr\anaconda3\lib\site-packages\livereload\server.py", line 291, in application
    app.listen(port, address=host)
  File "c:\users\epogr\anaconda3\lib\site-packages\tornado\web.py", line 2116, in listen
    server.listen(port, address)
  File "c:\users\epogr\anaconda3\lib\site-packages\tornado\tcpserver.py", line 151, in listen
    sockets = bind_sockets(port, address=address)
  File "c:\users\epogr\anaconda3\lib\site-packages\tornado\netutil.py", line 174, in bind_sockets
    sock.bind(sockaddr)
OSError: [WinError 10048] Only one usage of each socket address (protocol/network address/port) is normally permitted