Web launcher doesn't work on Windows

The code below is used to launch the web browser. The environment variable DISPLAY does not exist. Rather than having to create it, it should only use this environment variable on X Window based systems.

Maybe it should instead use if os.name == 'posix' :

```
def launch(url):
"""Attempt to launch the given URL."""
if os.environ.get('DISPLAY') is not None:
webbrowser.open(url)
return
```