Version 2.3.0

New features

• Allow manual definition of train/test set (add set=train/test after begin in
  input.data).
• Additional symmetry function log output, extra column spread.
• Structure remap() function is now available in pynnp.

Maintenance

• Fixed CI: Cython updated to version 3.0+, added __rmul__ to Vec3D in
  pynnp.

Important changes

• Synchronized LAMMPS developer build with LAMMPS-distributed source: Finally
  switched to pair style hdnnp everywhere.

Documentation

• Removed old nnp pair style description page.
• Updated LAMMPS interface build instructions page.
• Added train/test set split documentation.