parameterise the function to calculate startposition of weekly backup
change from 2-week rotation with 2 tapes, to 4-week rotation with 1 tape
merge and move main script functionality and config settings to backup_main.sh and backup_config.sh, and include them from the backup scripts
add installation section to readme file
add path of script when including
Merge branch 'dev' into tape-robot

Conflicts:
	backup.sh
	backup_archive.sh