v0.2.0 - changed shape definition and bugfixes

• 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