Fix single format compression

[marcospb19]

Now working for formats that are not archives.

This now works:

ouch compress LICENSE LICENSE.xz

Fixes #87.

[vrmiguel]

The new changes do work but I noticed that a there's a panic when decompressing these kinds of files to a new folder

# Works
❯ cargo run -- c src/main.rs main.rs.xz 

# Panics
❯ cargo run -- d main.rs.xz -o some-new-folder
thread 'main' panicked at 'No such file or directory (os error 2)', src/error.rs:173:45
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Although that's probably a matter for another issue

[marcospb19]

Sheesh, I will create another issue and merge this one to close #87 already.