Use namespace for OpenType tables

Avoids USHORT, SHORT, ULONG, LONG clashes with Windows API.
diff --git a/src/hb-open-type-private.hh b/src/hb-open-type-private.hh
index 4d8c507..4cbb855 100644
--- a/src/hb-open-type-private.hh
+++ b/src/hb-open-type-private.hh
@@ -34,6 +34,8 @@
 #include "hb-blob.h"
 
 
+namespace OT {
+
 
 /*
  * Casts
@@ -382,11 +384,6 @@
   DEFINE_SIZE_STATIC (sizeof (Type));
 };
 
-/* Typedef these to avoid clash with windows.h */
-#define USHORT	HB_USHORT
-#define SHORT	HB_SHORT
-#define ULONG	HB_ULONG
-#define LONG	HB_LONG
 typedef IntType<uint16_t> USHORT;	/* 16-bit unsigned integer. */
 typedef IntType<int16_t>  SHORT;	/* 16-bit signed integer. */
 typedef IntType<uint32_t> ULONG;	/* 32-bit unsigned integer. */
@@ -714,5 +711,7 @@
 };
 
 
+} // namespace OT
+
 
 #endif /* HB_OPEN_TYPE_PRIVATE_HH */