Create pull_genomes_as_genbank.py

Input on the command line your list of accesion numbers and this script will pull them down to your present working directory.  Requires python and biopython to work.  Example usage in unix terminal: 'python pull_genomes_as_genbank.py -a EU497054 DQ518969 EU517503 EF584003 -e mark.schultz@unimelb.edu.au -s gb', will pull four genbank files, one for each listed after the -a switch, and save them in '.gb' format. The -e switch is the user email address.  To get help, type 'python pull_genomes_as_genbank.py -h'.