Add RETURNING to Delete statement.

Add DELETE statement wiki page.

delete_statement_test.go

@@ -15,3 +15,11 @@ DELETE FROM db.table1
 WHERE table1.col1 = $1;
 `, int64(1))
 }
+
+func TestDeleteWithWhereAndReturning(t *testing.T) {
+	assertStatement(t, table1.DELETE().WHERE(table1Col1.EQ(Int(1))).RETURNING(table1Col1), `
+DELETE FROM db.table1
+WHERE table1.col1 = $1
+RETURNING table1.col1 AS "table1.col1";
+`, int64(1))
+}