Small text fixes
Initial import of abf_integrate
Add data consistency checks in abf_integrate
More consistent extended DOF force trajectory

Extended Lagrangian colvars now output applied and system forces
that are more consistent with non-extended ones, and more clearly
documented. Only affects the content of the colvar trajectory.
update LAMMPS code to match the current LAMMPS distribution
added simple makefile for colvartools
Update colvars ref paper
Merge branch 'master' of https://github.com/colvars/colvars