When a matching user joins a channel, send a text as a greeting
to the channel or the user. Normal greetings and random line
greetings are sent to the channel joined as a message. All
greetings are sent line buffered.
 
greeting     Send "greeting".
@greetfile   Send the entire contents of greetfile as private NOTICEs.
%greetfile   Pick a random line from greetfile as greeting.