Usage
-----
There are three commands `list`, `submit`, and `retrieve`.

    racket handin.rkt <command> ...

list: Lists available assignments open for submission.

    racket handin.rkt list

submit: Submits a file to the handin server for an assignment.

    racket handin.rkt submit <assignment> <filename>

retrieve: Retrieves a file from the server for an assignment.

    racket handin.rkt retrieve <assignment> <filename>

Dependencies
------------
Racket (only tested on 6.1)
PL plugin installed.