Adds a -v flag for ls(1), which sorts entries following a more natural ordering, rather than lexicographically ordering as it usually does (e.g. "ent1 ent2 ent10" as opposed to "ent1 ent10 ent2").
This is done through a strverscmp(3) function in libc, a GNU extension which I implemented by reading the glibc manual page for it.
I took the opportunity to also add a versionsort(3) function for scandir(3).
Manual pages updated for ls(1) & scandir(3), and adds a new manual page for strverscmp(3).
Adds tests for ls -v and strverscmp.