- modified the citeme reference (replaced by the JCP one)
- same modification in doc and src/SPIN

- created README in examples/SPIN
- modified doc/src/set.txt to define 'spin' and 'spin/random' keywords

update and clarify the choice of atom ids for angle style dipole (which is not really an angle potential)

changes to the energy only consider the kinetic energy, so make that explicit in the augmented `fix dt/reset` docs

Allow limiting of the maximum energy change of an atom in
fix dt/reset in addition to the existing distance limit.
Useful especially for high-energy irradiation.