Security issues when `sixel` feature is enabled

[orhun]

Currently, viuer suffers from the following security advisories:

• RUSTSEC-2022-0013
• RUSTSEC-2022-0006

$ cargo audit

Crate:     regex
Version:   0.1.80
Title:     Regexes with large repetitions on empty sub-expressions take a very long time to parse
Date:      2022-03-08
ID:        RUSTSEC-2022-0013
URL:       https://rustsec.org/advisories/RUSTSEC-2022-0013
Solution:  Upgrade to >=1.5.5
Dependency tree:
regex 0.1.80
└── semver-parser 0.6.2
    └── sixel 0.3.2
        └── viuer 0.6.1

Crate:     thread_local
Version:   0.2.7
Title:     Data race in `Iter` and `IterMut`
Date:      2022-01-23
ID:        RUSTSEC-2022-0006
URL:       https://rustsec.org/advisories/RUSTSEC-2022-0006
Solution:  Upgrade to >=1.1.4
Dependency tree:
thread_local 0.2.7
└── regex 0.1.80
    └── semver-parser 0.6.2
        └── sixel 0.3.2
            └── viuer 0.6.1

Both of these crates are reverse dependencies of the sixel crate which is outdated and unmaintained.

I looked at the codebase of sixel and realized these dependencies are not needed and removing them would fix these security issues. While I'm at it, I decided to maintain a fork of sixel since the maintainer is not that active on GitHub + they disabled issues on the repository.

That's why I created orhun/sixel-rs and I will be submitting a PR to switch to this crate. See the changelog here.