wall patch faces that each cell is potentially in range of.

which faces are from wall patches.

Moving ReferredCell into a subdirectory of ReferredCellList.

determines the number of subcycles needed to satisfy its timestep
requirements.

rotational kinetic energy monitoring function.

Currently the only supported model is fixing the temperature within the porous zone to a fixed value.

and amending by-component constuctors to accept them and f.

 - graham showed significant speedup (8-9x) for sqrt(sqrt(x)) compared to pow(x, 0.25)

everything is _AB, i.e. position, velocity and force wrt/on A from/by
B.

Using sqrt(sqrt()) instead of pow(..., 0.25) - quite a lot faster.