3D Engine upgraded to DirectX 9 for Compatibility

Hello,

I just upgraded the 3D Engine of Tennis Elbow 2013 from DirectX 8 to DirectX 9, which should prevent compatibility issues with GPU Drivers partially dropping DX8 support (especially on Windows 10) ; this should help people who have stuttering while playing.

Note: there's no visual change, it's only a compatibility update.

Also, the following feature has been added : Fullscreen Window mode ; this allows instant Alt+tab, and avoids crashes when changing FSAA and some other video settings unlike the exclusive fullscreen mode.

Changelog since release of the game on Steam can be read here : http://steamcommunity.com/app/346470/discussions/0/618456760265331075/ .