COREG / DESHIFTER: output format is now adjustable via keyword argument; Bugfix for wrong output filename

 COREG:
 - added keyword 'fmt_out' that allows to set the output format for deshifted data
 - improved docstring
 - Bugfix for missing output filename in case COREG had been instanced with default argument for path_out

 DESHIFTER:
 - added keyword 'fmt_out' that allows to set the output format for deshifted data
 - Bugfix for missing GeoArray in deshift_results in case align_grids=False

 MAIN:
 - updated default argument of '-o' option