#53 MinGW build fix

[Matt Clarkson]

This is a patch to solve false negatives when using CMake with MinGW.

The clock_t, clockid_t and timer_t types are deemed not found when they are actually available if time.h is included. The code compiles fine with MinGW and MSVC with this patch.

[Branden Archer]

Thanks for this patch, I've committed it. In addition your name will appear in the AUTHORS file for your help.

Thanks!