PG-PuReMD: merge memory management and step retry logic from MPI+GPU code into MPI-only code. Fix and backport numerous bugs (void pointer arithmetic and dereferences, etc.). Update code to match new data structures. Begin merging changes from OpenMP code (sPuReMD) for preconditioning work.

sPuReMD: make CoM logic consistent with PuReMD. Other build system updates for debugging and newer versions of MPICH.

sPuReMD: add checks on string and file handling. Rewrite PDB writing to be line-by-line. Other refactoring.

sPuReMD: remove debug prints. Default to no good initial guess for out of range values for spline extrapolation.

sPuReMD: move NaN checks on system energy to after logging. This allows better diagnostics for, e.g., the potential logging.

All: fix issue with pi bonds being incorrectly computed in bond orders. Patch originally submitted to LAMMPS mailing list by Tomas Trnka, SCM (refer to Issue #837 on Github).

sPuReMD: separate total energy computation and fix Python driver bug with structure definition for ctypes. Allow disabling file logging during simulation.

sPuReMD: refactor and clean up preconditioner application code (level scheduling, graph coloring, Jacobi iteration). Conditionally change charge matrix for setting up preconditioner for ICHOLT and ILU(T).

sPuReMD: fix issue with graph coloring causing sporadic failures in solver convergence for EE and ACKS2. Conditionally change the charge matrix for ICHOLT and ILU(T) preconditioning. Refactor graph coloring code.

sPuReMD: remove force tabulation for charge matrices. Revise list references to mirror MPI code. Revert GMRES iteration counter.