v3.0.0-beta.6

Added

• md.pair.LJ0804 - 8,4 Lennard-Jones pair potential.
• md.nlist.Stencil - Stencil algorithm to generate neighbor lists.
• md.nlist.Tree - BVH algorithm to generate neighbor lists.
• hoomd.md.Force, hoomd.md.Operation, and hoomd.md.Operations
  objects are now picklable.
• Manifold constraints using RATTLE with md.methods.NVE,
  md.methods.Langevin and md.methods.Brownian
  • Supporting sphere, ellipsoid, plane, cylinder, gyroid, diamond,
    and primitive manifolds.
• md.compute.HarmonicAveragedThermodynamicQuantities - More accurate
  thermodynamic quantities for crystals

Changed

• Raise an exception when initializing systems with invalid particle
  type ids.

Fixed

• Setting the operations attribute in Simulation objects in specific
  circumstances.
• Misc documentation updates.
• 'sim' is not defined error when using md.dihedral potentials.

Removed

• C++ implemtation of v2 logging infrastructure.