Added CellGrid eq to check compatibility of CellGrids
Added CellGrid eq to check compatibility of CellGrids

CellGrid views now a list

Moved address_to_index and index_to_address into CellGrid

CellGrid getitem allows a tuple

Added half and full neighbour generation to Cells.
Now returns addresses not actual Cells

richardjgowers/cellgrid,MDAnalysis/cellgrid