parsers: add umbrella enum for SASL elements

This is useful if, for example during stream negotiation, you want to
parse SASL elements and nothing else. It is also useful if you want to
write down an enum of all XMPP-related stream-level elements you accept
and don't want to loose your fingers typing all the SASL options.

parsers/src/sasl.rs

@@ -163,6 +163,35 @@ pub struct Failure {
     pub texts: BTreeMap<Lang, String>,
 }
 
+/// Enum which allows parsing/serialising any SASL element.
+#[derive(FromXml, AsXml, Debug, Clone)]
+#[xml()]
+pub enum Nonza {
+    /// Abortion of SASL transaction
+    #[xml(transparent)]
+    Abort(Abort),
+
+    /// Failure of SASL transaction
+    #[xml(transparent)]
+    Failure(Failure),
+
+    /// Success of SASL transaction
+    #[xml(transparent)]
+    Success(Success),
+
+    /// Initiation of SASL transaction
+    #[xml(transparent)]
+    Auth(Auth),
+
+    /// Challenge sent by the server to the client
+    #[xml(transparent)]
+    Challenge(Challenge),
+
+    /// Response sent by the client to the server
+    #[xml(transparent)]
+    Response(Response),
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;