Usage: .tell {<user>|@[group]}[,[-]{<user>|@<group>}[,...]] <message>

Allows you to send a message to another user or group, or multiple
groups and users. This can be abbreviated to just '>'.

Examples:
.tell @public Hello you lot!             -- Just tells group Public.
.tell @public,-foo Foo smells.           -- Tells everybody but foo.
.tell foo,bar,oink Hello!                -- Tells foo, bar, and oink.
.tell foo Hello!                         -- Tells just foo.