Improved XML serialization

- Use quick_xml and serde for all XML response returned by the S3 API.
- Include tests for all structs used to generate XML
- Remove old manual XML escaping function which was unsafe

src/util/time.rs

@@ -16,5 +16,5 @@ pub fn msec_to_rfc3339(msecs: u64) -> String {
 	let secs = msecs as i64 / 1000;
 	let nanos = (msecs as i64 % 1000) as u32 * 1_000_000;
 	let timestamp = Utc.timestamp(secs, nanos);
-	timestamp.to_rfc3339_opts(SecondsFormat::Secs, true)
+	timestamp.to_rfc3339_opts(SecondsFormat::Millis, true)
 }