======Synopsis:======
[[on]] [<modes>]nickname [<serial#>] [-|^]<match> { <action> }

======Description:======
This hook is triggered whenever the client observes a nickname change.
It only hooks once per nick change, not once per channel.

======Parameters:======
|$0 |old nickname|
|$1 |new nickname|

======Examples:======
To distinguish the client from another user:
   on ^nickname "*" {
      if ( [$0] == N ) {
         xecho -b Your nickname is now $1
      } {
         xecho -b $0 has changed nicks to $1
      }
   }