Detect IE on ARM as tablet

This adds a couple checks such that Internet Explorer running on ARM platforms (excluding Windows Phone) is identified as a tablet system. At this time, only Windows RT would be running Internet Explorer on the ARM platform. User agent strings can be found in documentation at http://msdn.microsoft.com/en-us/library/ie/hh920767(v=vs.85).aspx and tested on a Windows RT device (Surface).

Fixes #53