new package: gsl the GNU Scientific Library.

[thomas.petazzoni@free-electrons.com:
 renamed package to 'gsl' to match upstream name.
 added license information.]

Signed-off-by: Sagaert Johan <sagaert.johan@skynet.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>