Allow moving files to sub-directories

This release allows moving files to sub-directories by adding a directory before a filename. For example, this

one.txt
two.txt
three.txt

renamed to this:

a/one.txt
a/two.txt
b/three.txt

will move the files "one.txt" and "two.txt" to the directory "a", and "three.txt" to the "b". If any of these directories do not exist they will be automatically created.