xmpp-parsers: Parse the bind feature in its module, with required

This is different from the bind query or the bind response, despite all
three having the same element namespace and name…  Annoying!

parsers/src/bind.rs

@@ -10,6 +10,20 @@ use crate::iq::{IqResultPayload, IqSetPayload};
 use crate::ns;
 use jid::{FullJid, Jid};
 
+/// The bind feature exposed in stream:features.
+#[derive(FromXml, AsXml, Debug, Clone, PartialEq)]
+#[xml(namespace = ns::BIND, name = "bind")]
+pub struct BindFeature {
+    /// Present if bind is required.
+    #[xml(child(default))]
+    required: Option<Required>,
+}
+
+/// Notes that bind is required.
+#[derive(FromXml, AsXml, Debug, Clone, PartialEq)]
+#[xml(namespace = ns::BIND, name = "required")]
+pub struct Required;
+
 /// The request for resource binding, which is the process by which a client
 /// can obtain a full JID and start exchanging on the XMPP network.
 ///
@@ -68,6 +82,8 @@ mod tests {
     #[cfg(target_pointer_width = "32")]
     #[test]
     fn test_size() {
+        assert_size!(BindFeature, 1);
+        assert_size!(Required, 0);
         assert_size!(BindQuery, 12);
         assert_size!(BindResponse, 16);
     }
@@ -75,6 +91,8 @@ mod tests {
     #[cfg(target_pointer_width = "64")]
     #[test]
     fn test_size() {
+        assert_size!(BindFeature, 1);
+        assert_size!(Required, 0);
         assert_size!(BindQuery, 24);
         assert_size!(BindResponse, 32);
     }