Update memo struct to use the additional structure as memo item inste…

…ad of embedded structure (#77)

data/memo.go

@@ -1,11 +1,13 @@
 package data
 
+type MemoItem struct {
+	MemoType   VariableLength
+	MemoData   VariableLength
+	MemoFormat VariableLength
+}
+
 type Memo struct {
-	Memo struct {
-		MemoType   VariableLength
-		MemoData   VariableLength
-		MemoFormat VariableLength
-	}
+	Memo MemoItem
 }
 
 type Memos []Memo