Move Error, helpers and macros into a util module.

src/date.rs

@@ -4,7 +4,7 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-use crate::error::Error;
+use crate::util::error::Error;
 use chrono::{DateTime as ChronoDateTime, FixedOffset};
 use minidom::{ElementEmitter, IntoAttributeValue, IntoElements};
 use std::str::FromStr;