Find and restrain rings

[d=1.39] [esd=0.01] ring_content or selection

Finds rings using the selection or rings content (like C6). It also sets DFIX restraint for the bond lengths using the d parameter and FLAT with e.s.d. of 0.1 restraint for the ring. It also adds SADI restraints for the 1-3 distances. If d is negative, the SADI restraint is used instead.