#43 adding method Nansat.crop
#43 nansat-crop modify SrcRect and DstRect
#48 #51 VRT.get_super_vrt remove PixelFunction from Metadata, Nansat.crop add news GCPs, Domain._tranform_points moved to VRT.transfrom_points, Domain._get_rpojection moved to VRT.get_projection; croping and resize works for RS2
Merge branch 'issue43-nansat-crop' into issue38