This script will SUBSCRIBE to the presence event published by the specified
SIP target assuming it is a resource list handled by a RLS server. The RLS
server will then SUBSCRIBE in behalf of the account, collect NOTIFYs with the
presence information of the recipients and provide periodically aggregated
NOTIFYs back to the subscriber. If a target address is not specified, it will
subscribe to the account's own address. It will then interprete PIDF bodies
contained in NOTIFYs and display their meaning. The program will un-SUBSCRIBE
and quit when CTRL+D is pressed.