Feature: Add the Discrete GPU force header for use in executables.

[guestnone]

This header file when included on final executable is used on Windows-based computers to force the laptops with NVIDIA Optimus or AMD Xpress features to use discrete GPU's instead of the Intel integrated graphics chip.

Solves issue #236 (at least on Windows, Linux probably works differently).

[BearishSun]

Thanks. I need to consider if there's a better way of doing this, I don't like the idea the users need to remember to add a header manually. If I can't think of anything I'll merge.