Function: simpleMailbox

CALL:

messages = simpleMailbox(username) messages = simpleMailbox(username, message)

DESCRIPTION:

Retrieve and send messages for use "username"

INPUT:

username string
identity of sender or receiver.
message any
data to be sent. If not specified then retrieve messages for
"username" otherwise send message.

OUTPUT:

messages cell[]
With all undelivered messages for "username"