quick and dirty windows port

d:\kit\pthreads-win32-VC-x64\ is where the pthreadVC2.lib,
pthreadVC2.dll and pthread.h reside on my system. User should be able to
specify the header file location, library name and library location via
config attributes or environment variable (or better yet, code should be made portable, perhaps by using C++11 standard threading classes).

Also, defines that trigger symbol exporting should be passed as -D args to compiler.