-DLMP_USE_LIBC_QSORT will use qsort() from libc to sort (requires static/global variables).
-DLMP_USE_MERGE_SORT will use a plain merge sort. slightly slower for expensive comparisons.
-DLMP_USE_HYBRID_SORT will use hybrid merge sort. faster than merge sort (no static/global variables)

- use insertion sort to pre-sort data in 32-element chunks
- swap pointers between merge runs instead of copying the data

The dump and irregular classes were using qsort() from the C-library
for sorting lists through custom comparison functions, which required
access to additional data, which was passed via static class variables,
i.e. globals. This collides with having multiple LAMMPS instances in
the same address space.

the calls to qsort() are replaced with a custom merge sort, which passes
a void pointer to the comparison functions, which can contain any kind
of desired information, e.g. a class handle or a list

SNAP changes by Aidan

Collection of minor updates

Fix bug where fix/compute style names were not correctly set with suffixes

Collected small updates and bugfixes

Using correct value for atom->nlocal in translate/rotate in fix_gcmc.cpp

Setting molecule COM to 0 after moving atoms

must not use strtok() in library function as it is not re-entrant and may be used inside LAMMPS commands

Doc and example fixes