Merge pull request #41 from lammps/master

doc/src/fix_bond_react.txt

src/KOKKOS/pair_snap_kokkos_impl.h

src/KOKKOS/sna_kokkos_impl.h

src/MOLECULE/improper_umbrella.cpp

src/USER-MISC/fix_bond_react.cpp

src/USER-MISC/fix_bond_react.h

src/USER-MISC/improper_fourier.cpp

src/USER-OMP/improper_fourier_omp.cpp

src/USER-OMP/improper_umbrella_omp.cpp