previously had incorrect logic for checking if fix is acceptable

- re-indent to 2 blanks
- white space cleanup
- use force->numeric() and force->inumeric() instead of atof() and atoi()
- include system headers before local LAMMPS headers

adapt formatting and naming conventions to fully match LAMMPS style. allow rigid and accelerated integrators.

Updated command to temper/npt instead of temper_npt

change ring communication API to no longer require a static variable pointing to 'this' of the caller