lib: addd nitunits to Numeric::value_of

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/geometry: intro the contructor Box::around

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/geometry: refactor implementation of contains and intersects in 3d

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>