Quotation marks aren't being detected properly within the iotile cmdline on Windows

On Windows (The LabPC), using PowerShell, and tried to force a proxy when connecting to the controller of my Access Point. Here's the command and error:

```
(venv) PS C:\Users\LabUser\tfroehlich> iotile hw --port=bled112
(HardwareManager) connect 0x12d2
(HardwareManager) get 8 --force='NRF52 '
Traceback (most recent call last):
File "c:\users\labuser\tfroehlich\venv\lib\site-packages\iotile\core\scripts\iotile_script.py", line 244, in main
finished = shell.invoke_string(linebuf)
File "c:\users\labuser\tfroehlich\venv\lib\site-packages\typedargs\shell.py", line 517, in invoke_string
args = self._split_line(line)
File "c:\users\labuser\tfroehlich\venv\lib\site-packages\typedargs\shell.py", line 136, in _split_line
parts = shlex.split(line, posix=self.posix_lex)
File "C:\Users\LabUser\tfroehlich\python3.7\Lib\shlex.py", line 310, in split
return list(lex)
File "C:\Users\LabUser\tfroehlich\python3.7\Lib\shlex.py", line 299, in __next__
token = self.get_token()
File "C:\Users\LabUser\tfroehlich\python3.7\Lib\shlex.py", line 109, in get_token
raw = self.read_token()
File "C:\Users\LabUser\tfroehlich\python3.7\Lib\shlex.py", line 191, in read_token
raise ValueError("No closing quotation")
ValueError: No closing quotation
(HardwareManager)
```

The same command sequence worked fine on my Linux PC :
```
$ iotile hw
(HardwareManager) connect 42
(HardwareManager) get 8 --force='NRF52 '
(NRF52832Controller)
```

The windows test was with Python 3.7 and I got the same results with the Python test with both Python 3.7 and 3.5.

The workaround is to get the proxy from an initial command line invocation, which works properly.
` iotile hw --port=bled112 connect 0x12d2 get 8 --force='NRF52 '`