Renaming 'r' to 'alea'

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
Correcting exit codes

The valid exit code are form 0 to 255. Then using -1 means that the
effective exit code will be 0377==255. It isn't accurate. The exit code
of 1 is merely very often used for failure status.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
Adding some comments

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>
Adding a usage function.

Signed-off-by: José Bollo <jose.bollo@open.eurogiciel.org>