Add integer attribute type.

Merges some common code between integer and enum.
Enum can now bw a set.
Add valuer must take a interface{} in addValue since it can be different types.

packages/ipp/keyword.go

@@ -31,7 +31,7 @@ func (k *keyWord) marshal() []byte {
 	return k.sos.marshal()
 }
 
-func (k *keyWord) addValue(v string) {
-	k.sos.AddValue(v)
+func (k *keyWord) addValue(v interface{}) {
+	k.sos.AddValue(v.(string))
 }