Converted the rest of the obj_*.h headers to IDL into shobjidl.idl.

diff --git a/include/wtypes.h b/include/wtypes.h
index ae79eff..4a1950b 100644
--- a/include/wtypes.h
+++ b/include/wtypes.h
@@ -76,6 +76,8 @@
 
 typedef void *HKEY;
 
+typedef void *HICON;
+
 typedef LONG_PTR LRESULT;
 
 typedef double DATE;