[MMTK] Convert LAMMPS MD trajectory to netCDF format with MMTK convention for nMoldyn analysis.

[Yi Liu]

Hi, Jay and Konrad,

Thanks for the trj_to_nc.py script from Jay. This script helps me to
write a converter for LAMMPS trajectory using SnapshotGenerator from
MMTK.

Thanks Konard for all your comments and suggestions.

Yi