- Move the 3 public headers to a include directory.
+ pthreads ships a config.h therefore leaving them in the top dir
pollutes the include path.
- Starting with VS2015, MS defines timespec. Declare to only have it
if _MSC_VER >= 1900.
- On Linux pthread_t is an integer and you can easily do ==. On Windows
pthread_t is a structure and ==/!= have to be overloaded or every use of
those operator must be guaded with #ifdef's.