v3.0.0-beta.13

Added

• md.pair.ExpandedLJ - A Lennard-Jones potential where r is
  replaced with r-delta.
• Support nested modification of operation parameters.
• wall - Define wall surfaces in the simulation box.
• md.external.wall - Pair interactions between particles and wall
  surfaces.
• Communicator.walltime - the wall clock time since creating the
  Communicator.
• hoomd.md.force.Custom - user defined forces in Python.

Changed

• Call update_group_dof implicitly in set_snapshot, when changing
  integrators or integration methods, and on steps where
  FilterUpdater acts on the system.
• [breaking] update_group_dof defers counting the degrees of
  freedom until the next timestep or the next call to
  Simulation.run.
• [breaking] Renamed md.bond.FENE to md.bond.FENEWCA.
• md.bond.FENEWCA takes a user provided delta parameter and
  ignores the particle diameters.
• [breaking] md.pair.DLVO takes user provided a1 and a2
  parameters and ignores the particle diameters.
• Removed invalid linker options when using gcc on Apple systems.
• Removed the r_on attribute and default_r_on constructor argument
  from pair potentials that do not use it.

Fixed

• Compile error with Apple clang clang-1300.0.29.30.
• Incorrect OPLS dihedral forces when compiled with
  Apple clang clang-1300.0.29.30.

Deprecated

• md.pair.SLJ - Replaced with md.pair.ExpandedLJ.

Removed

• Leftover state logging category.