Revert "removed windows". Refs #698.

This reverts commit 5ab3d66144.

examples/wingui.nim

@@ -0,0 +1,9 @@
+# test a Windows GUI application
+
+import
+  windows, shellapi, nb30, mmsystem, shfolder
+
+#proc MessageBox(hWnd: int, lpText, lpCaption: CString, uType: uint): int
+#  {stdcall, import: "MessageBox", header: "<windows.h>"}
+
+discard MessageBox(0, "Hello World!", "Nimrod GUI Application", 0)