Standard arguments for convert/generate scripts

[SamPUG]

This issue is added in response to a requirement from @shimwell and @ukaea.

There are currently different arguments used in each of the scripts. Some of them use --download while others use --batch. The arguments for each script should be standardised as discussed in #8.

I am planning to replace the --batch argument in all relevant scripts with the same argument format as the JEFF scripts, eg:

parser.add_argument('--download', action='store_true',  
                    help='Download files from OECD-NEA')
parser.add_argument('--no-download', dest='download', action='store_false',
                    help='Do not download files from OECD-NEA')
parser.add_argument('--extract', action='store_true',
                    help='Extract tar/zip files')
parser.add_argument('--no-extract', dest='extract', action='store_false',
                    help='Do not extract tar/zip files')

[shimwell]

Yes please this would be great as it is a bit of inconstant at the moment

Once this is done I might even be tempted to update the readme :-)

[paulromano]

Closed with #26