New Formula: LAMMPS (requested in #45)

LAMMPS:
"Large-scale Atomic/Molecular Massively Parallel Simulator"

* Lammps binary, library, and python module are installed
* Both serial and mpi parallelized versions are available
* Docs, examples, tools, and benchmark scripts are installed
* All standard packages are installed (2 are currently disabled)
* User packages are available as options (2 are currently disabled)