bug: fixed #74 by shifting the geometry, possibly rescaling it.
bug: fixed #74 by shifting the geometry, possibly rescaling it.

Now a Grid.<change> will do one of 2 things:

1) If the Grid is changed in a non-consistent manner, i.e. sum/average
or a non-consecutive subset of indices are retained the geometry coordinates
will be rescaled according to the new supercell.

2) If the subset indices are consecutive the resulting geometry will
   be shifted according to the minimum new indices in the grid.
   This will still retain atoms outside the new unit-cell, if present.

TODO remove atoms outside the retained region.

Signed-off-by: Nick Papior <81a73bca3d342ffee33d7cf845fdbf77b6553831@gmail.com>

zerothi/sisl,zerothi/sisl