on [<modes>]invite [<serial#>] [-|^]<match> { <action> }
This hook is triggered whenever the client receives an invitation to a channel.
| $0 | nickname inviting the client to a channel | 
| $1 | channel invited to | 
Customizing the appearance of the invitation:
 on ^invite "*" {
    xecho -b $0 cordially invites you to $1
 }