Add export LAMMPS binary dump

Hey,

binary files are much faster to parse. Often it would be nice to export binary dump files so it can be imported at a later stage (i.e. convert text dump file produced with append yes which is not supported for binary files in LAMMPS).

We have implemented this for in-house use, so we could add an MR if you want, or you could work on it yourself.

What do you think?