`cmp` command is not implemented

[oSoMoN]

Currently uutils' diffutils only implements the diff executable.

But GNU's diffutils also provide cmp, diff3 and sdiff.

This issue is a tracker for the implementation of the cmp utility.

Documentation: https://www.gnu.org/software/diffutils/manual/html_node/Invoking-cmp.html.

[keys-i]

i have made a separate file cmp.rs

[keys-i]

and implemented a basic cmp with no fuzzing yet

[keys-i]

for cmp testing would be have some dummy files?

[kov]

I've submitted an implementation of cmp here https://github.com/uutils/diffutils/pull/88