new CHARMM pair styles with force swithing/shifting

doc/src/Section_commands.txt

doc/src/Section_example.txt

doc/src/Section_howto.txt

doc/src/compute_modify.txt

doc/src/dihedral_charmm.txt

doc/src/kspace_style.txt

doc/src/pair_charmm.txt

doc/src/pair_momb.txt

examples/README

examples/gcmc/CO2.txt

examples/gcmc/in.gcmc.co2

examples/gcmc/in.gcmc.lj

examples/gcmc/log.24Mar17.gcmc.co2.g++.1

examples/gcmc/log.24Mar17.gcmc.co2.g++.4

examples/gcmc/log.24Mar17.gcmc.lj.g++.1

examples/gcmc/log.24Mar17.gcmc.lj.g++.4

src/KSPACE/pair_lj_charmmfsw_coul_long.cpp

src/KSPACE/pair_lj_charmmfsw_coul_long.h

src/MANYBODY/pair_airebo.cpp

src/MOLECULE/dihedral_charmmfsh.cpp