Highlight some built-in types from object.d(i).

These are enabled when d_hl_object_types is defined.

d.vim

@@ -69,6 +69,10 @@ syn keyword dType                  float double real
 syn keyword dType                  void ushort int uint long ulong float
 syn keyword dType                  char wchar dchar string wstring dstring
 syn keyword dType                  ireal ifloat idouble creal cfloat cdouble
+if exists("d_hl_object_types")
+  syn keyword dType                size_t ptrdiff_t sizediff_t equals_t hash_t
+  syn keyword dType                Object Throwable AssociativeArray
+endif
 syn keyword dDebug                 deprecated unittest invariant
 syn keyword dExceptions            throw try catch finally
 syn keyword dScopeDecl             public protected private export package