geo.raster.reproject:
- warp_ndarray(): added output assertion

geo.projection:
- prj_equal(): added better docstring

io.raster.GeoArray:
- GeoArray:
    - revised mask_nodata property
    - added assertion to footprint_poly
    - revised calc_mask_nodata()
-_clip_array_at_mapPos(): bugfix for missing fillVal in case nodata value could not be derived