s2y, s2z, z2s and y2s: allow a different ref impedance for each port

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>
add missing y2z and z2y

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>
s-parameter re-normalize

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>
new network calculation functions

Signed-off-by: Thorsten Liebig <Thorsten.Liebig@gmx.de>