New features:

- The Amber12SB force field is implemented in addition to Amber94 and Amber99.

- New restraint term: HarmonicTrapForceField restrains the center of mass
  of an object to a fixed point in space using a spring term.

- HarmonicDistanceRestraint now accepts non-atom objects, applying the
  restraint between their centers of mass. A distance restraint can optionally
  be treated like a chemical bond, suppressing any non-bonded interactions
  between the same pair of atoms.

- The Amber parameter files have been updated to the versions contained
  in AmberTools 12.


Removed features:

- The DPMTA library and its MMTK interface code, implementing the
  multipole method for electrostatic interactions, has been removed.
  The MMTK interface has been unusable for years due to a typo that
  made it crash. No one ever complained, so it seems safe to assume that
  nobody uses it. DPMTA has become an obstacle to the distribution and
  packaging of MMTK because it doesn't have a clear licence.

Improvements:

- The visualization interface under MacOSX and Linux has been modified.
  When no PDBVIEWER is defined, it defaults to the system mechanism for
  opening PDB or VRML files, which is "open" under MacOSX and "xdg-open"
  under Linux.