Checking for Windows support

Hi,

I'm using SimpleProgressbar in an Windows Environment. Therefor I'm checking whether 'win32console' gem was installed, because otherwise the console output will be kind of strange ;-)

![consoleoutput](https://f.cloud.github.com/assets/1001764/612012/15eaa8f2-cde4-11e2-8e75-f1f7faec5b72.png)

Regards