Add contrast options

<!-- Wait! Before reporting a bug: - Check the FAQ: https://ntsc.rs/docs/faq/ - Make sure you have followed the installation instructions: https://ntsc.rs/docs/standalone-installation/ - Make sure you are running the latest version of ntsc-rs: https://github.com/valadaptive/ntsc-rs/releases - Make sure your OS is up-to-date - Search the Issues section to see if the bug has already been reported, and if it has, leave a comment on that issue instead: https://github.com/valadaptive/ntsc-rs/issues In particular, ntsc-rs does *not* run on Windows 7 (see the FAQ for more info). --> **Describe the bug** <!-- A clear and detailed description of what the bug is. --> **To Reproduce** <!-- Steps to reproduce the behavior. If the bug occurs when working with a specific image or video, attach it here, *in its original format*. --> **Screenshots/Screen Recordings** <!-- If at all possible, attach a screen recording (or screenshot) demonstrating the bug. --> **Platform Information** <!-- Operating system + version (for example, Windows 10 22H2, macOS 13.7.5, Ubuntu 22.04) --> I think adding contrast options would be nice, considering that vhs and ntsc has contrast problems