Implement Korlib API versioning

A common error when developing with Korman and Korlib is to forget to
recompile _korlib on changes in the upstream C++ code. This will prevent
the errors from being catastrophic and will revert the user to the
python reference implementation with a minimum of fuss.

korlib/module.cpp

@@ -18,6 +18,9 @@
 #include "sound.h"
 #include "texture.h"
 
+// This konstant is compared against that in the Python module to prevent sneaky errors...
+#define KORLIB_API_VERSION 1
+
 extern "C" {
 
 static PyMethodDef korlib_Methods[] = {
@@ -46,6 +49,9 @@ PyMODINIT_FUNC PyInit__korlib() {
     // Module classes...
     PyModule_AddObject(module, "GLTexture", Init_pyGLTexture_Type());
 
+    // Konstants
+    PyModule_AddIntConstant(module, "_KORLIB_API_VERSION", KORLIB_API_VERSION);
+
     return module;
 }