geo.coord_grid:
- find_nearest_grid_coord(): fixed inconsistency regarding key 'SE' vs. 'SO'

io.raster.GeoArray.GeoArray:
- __init__():
    - added docstring
    - init parameters are now respected in case GeoArray is instanced from another GeoArray
    - moved some parameter settings to separate properties
- attributes 'arr' and 'bandnames' are now properties
- revised propery 'shape'
- show(): added warning
- added deepcopy_array()