Add support for Windows (ImportError: No module named fcntl)

Hello!

I have seen a few tickets related to windows support that have been closed. Since they are closed, I am making the assumption that people have figured out fixes that I may not be realizing. Could someone point me in the right direction?

Related Issue(s)
https://github.com/cs01/gdbgui/issues/18

At the root of this, I am trying to run guincorn on windows 10 using Cygwin

I have successfully upgraded gdbgui (pip install gdbgui --upgrade)
gdbgui==0.13.2.0

```
$ gunicorn
Traceback (most recent call last):
File "C:\Users\jz\AppData\Local\Programs\Python\Python37\Lib\runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "C:\Users\jz\AppData\Local\Programs\Python\Python37\Lib\runpy.py", line 85, in _run_code
exec(code, run_globals)
File "C:\Users\jz\.virtualenvs\venv-Z2lewwtS\Scripts\gunicorn.exe\__main__.py", line 5, in
File "c:\users\jz\.virtualenvs\venv-z2lewwts\lib\site-packages\gunicorn\app\wsgiapp.py", line 9, in
from gunicorn.app.base import Application
File "c:\users\jz\.virtualenvs\venv-z2lewwts\lib\site-packages\gunicorn\app\base.py", line 12, in
from gunicorn import util
File "c:\users\jz\.virtualenvs\venv-z2lewwts\lib\site-packages\gunicorn\util.py", line 9, in
import fcntl
ModuleNotFoundError: No module named 'fcntl'

```