planets.f90: saturnphys(): return physical data from pov of the Sun

* planets.f90: saturnphys(): return physical data from pov of the Sun:
  * pa_s: position angle of Saturn's axis
  * ar_s: the major axis of the ring
  * br_s: the minor axis of the ring
Added two output variables to subroutine jupiterphys()

* Added two output variables to subroutine jupiterphys():
  * in: Inclination of Jupiter's rotation axis to the orbital plane
  * om: Longitude of node of Jupiter's equator on ecliptic
Added two output variables to subroutine saturnphys()

* Added two output variables to subroutine saturnphys():
  * in: Inclination of Saturn's rotation axis to the orbital plane
  * om: Longitude of node of Saturn's equator on ecliptic
Updated some comments