Comms

The comms module handles all of the communications in Castep, and comes in two flavours at the moment: serial and MPI. The work in comms boils down to:

• Create a new communicator for the new `band-groups'.
• Create new comms_reduce and comms_copy routines to support reduction/copying of data over the band-groups.

In particular the subroutines comms_parallel_strategy and comms_reassign_strategy now need to know how many bands to parallelise over, and so has gained an additional mandatory argument `nbands'. This has necessitated trivial changes to model.F90 and castep.f90.

Work completed, tested and working.