`unic` is unmaintained

[Finomnis]

There was a rustsec advisory about unic being unmaintained.

It seems to be used in literal/Cargo.toml and parser/Cargo.toml.

Solution: Replace with something maintained, see the rustsec advisory link for suggestions.

[fanninpm]

The RustPython project is now using Ruff's parser instead of this crate.

@youknowone should we update the README to that effect?

[youknowone]

Sure, I think it would be better to archive this repository.

With notice that anyone can freely fork it in different name. (to prevent confusion to our current parser)

[Finomnis]

@fanninpm @youknowone Can you hereby officially declare this crate as unmaintained then? Then I'll add is as such into the rustsec advisory database.