OK, a new version. This has tidied up a couple of things that were annoying me.

I have also added the ability to perform FILE or FILEGROUP backups. This only works if you specify a single database name. You can specify multiple files or filegroups. Supports FULL and DIFFERENTIAL backups for all.

I [believe I] have fully tested it, but there's always a chance I have missed something. If you have any problems, let me know.