Put feature access in spot accessor.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Spots can be added incrementally.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Use a realistic version number.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>