natural sort

[BenjaminKobjolke]

I have a list of files like this:
test1.txt
test10.txt
test2.txt
test3.txt
test4.txt
test5.txt
test6.txt
test7.txt
test8.txt
test9.txt

I want to rename them to
document_01.txt
document_02.txt
....

But I can't sort the files in a way that test10.txt is the last file.

Solution:
Add support for --sort natural

https://en.wikipedia.org/wiki/Natural_sort_order