How to change the default port

Hi, #32 #33 Related to these two issues. Still don't know how to change the default port. I was using excalibular 0.4.2. I changed the web_server_port in default_excalibur.cfg, but doesn't solve this problem. The error message is as below:
```
* Serving Flask app "excalibur.www.app" (lazy loading)
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
Traceback (most recent call last):
File "c:\apps\anaconda3\Lib\runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "c:\apps\anaconda3\Lib\runpy.py", line 85, in _run_code
exec(code, run_globals)
File "C:\Users\cliu\Desktop\demo\table\excaliburPython\Scripts\excalibur.exe\__main__.py", line 7, in
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\click\core.py", line 764, in __call__
return self.main(*args, **kwargs)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\click\core.py", line 717, in main
rv = self.invoke(ctx)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\click\core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\click\core.py", line 956, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\click\core.py", line 555, in invoke
return callback(*args, **kwargs)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\excalibur\cli.py", line 60, in webserver
use_reloader=False)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\flask\app.py", line 990, in run
run_simple(host, port, self, **options)
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\werkzeug\serving.py", line 1010, in run_simple
inner()
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\werkzeug\serving.py", line 963, in inner
fd=fd,
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\werkzeug\serving.py", line 806, in make_server
host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd
File "c:\users\cliu\desktop\demo\table\excaliburpython\lib\site-packages\werkzeug\serving.py", line 699, in __init__
HTTPServer.__init__(self, server_address, handler)
File "c:\apps\anaconda3\Lib\socketserver.py", line 453, in __init__
self.server_bind()
File "c:\apps\anaconda3\Lib\http\server.py", line 136, in server_bind
socketserver.TCPServer.server_bind(self)
File "c:\apps\anaconda3\Lib\socketserver.py", line 467, in server_bind
self.socket.bind(self.server_address)
OSError: [WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions
```

Start at excalibur/cli.py around the webserver entry point shown in the traceback, then inspect how web_server_port is read from default_excalibur.cfg. Reproduce the Windows startup failure and determine whether the documented configuration changes the port; done means users can follow clear instructions to select a working port.

Written by the indexing model from the issue text.