check $::operatingsystem => windows otherwise fail
* limit module usage for Windows 2008 R2 and newer versions of Windows
* spec tests for different kernel versions
* Windows 2012 and newer uses 'Install-Windowsfeature' instead of 'Add-Windowsfeature'
Merge pull request #12 from shoekstra/windows_only_and_windows2012

Windows support only and updated Windows 2012 cmdlet