Pygeogrids

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- Fix bug in calc_lut in case of differently ordered subset of a grid.
- Add function to reorder grid based on different cell size. (See grids.reorder_to_cellsize)

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- Add option to load grids with non standard variable name for gpis.

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- Fix bug in gpi2lonlat with subset, see 42
- Add simple script for plotting a global cell partitioning.

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- fix bug in storing/loading grids with shape attribute set.
- change equality check of grids to be more flexible. Now only a match of the
tuples gpi, lon, lat, cell is checked. The order does no longer matter.
- Shape definition changed to correspond to what one would expect. Now a 1x1
regular global grid has the shape (180, 360) corresponding to the 180 rows and
360 columns that the array has. This was necessary since the genreg_grid
function produced grids with wrong lon2d, lat2d arrays because the shape was
not correct

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- bugfix in lonlat2cell. Improvements in dependency installation and
documentation.

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- bugfix in gpi2lonlat. Now supports array as input.