xso-proc: add fancy hack to allow codec = Foo<Bar>

We can do this because we know that `x < y` cannot create a
`TextCodec<T>` for any `T`. This is because `<` is guaranteed to return
a boolean value, and we simply don't implement `TextCodec<T>` on bool.

parsers/src/component.rs

@@ -20,7 +20,7 @@ pub struct Handshake {
     ///
     /// If None, it is the successful reply from the server, the stream is now
     /// fully established and both sides can now exchange stanzas.
-    #[xml(text(codec = FixedHex::<20>))]
+    #[xml(text(codec = FixedHex<20>))]
     pub data: Option<[u8; 20]>,
 }
 

parsers/src/vcard_update.rs

@@ -30,7 +30,7 @@ pub struct VCardUpdate {
 #[xml(namespace = ns::VCARD_UPDATE, name = "photo")]
 pub struct Photo {
     /// The SHA1 hash of the avatar. Empty when there is no photo.
-    #[xml(text(codec = FixedHex::<20>))]
+    #[xml(text(codec = FixedHex<20>))]
     pub data: Option<[u8; 20]>,
 }