a HUGE amount of difficult to resolve and understand conflicts .
Wholesale formatting, reordering functions etc... in a central file like Tensor_class
or Grid_vector_types while others are also editing without making substantial functionality
changes creates pain.
preparing to pass integrator, smearing, bc's as policy classes to hmc.
Propose to unify "integrator" and integrator algorithm in a base/derived
way to override step. Want to read through ForceGradient to ensure
that abstraction covers the force gradient case.
