Make the relay acknowledge all received commands

To that effect, bump liberty and the xC relay protocol version.
Relay events have been reordered to improve forward compatibility.

Also prevent use-after-free when serialization fails.

xP now slightly throttles activity notifications,
and indicates when there are unacknowledged commands.

NEWS

@@ -1,3 +1,15 @@
+Unreleased
+
+ * xC: added more characters as nickname delimiters,
+   so that @nick works as a highlight
+
+ * xC: prevented rare crashes in relay code
+
+ * xP: added a network lag indicator to the user interface
+
+ * Bumped relay protocol version
+
+
 2.1.0 (2024-12-19) "Bunnyrific"
 
  * xC: fixed a crash when the channel topic had too many formatting items