Unified getitem output for all tilers

Unified getitem output for all tilers: ConstStrideTiles, ConstSizeTiles

tiles = ConstSizeTiles(*args, **kwargs)
for extent, out_size in tiles:
    pass

and

tiles = ConstStrideTiles(*args, **kwargs)
for extent, out_size in tiles:
    pass

Please, note that in the previous version ConstSizeTiles provides only extent:

tiles = ConstSizeTiles(*args, **kwargs)
for extent in tiles:
    pass