Fix operating system versions in GitHub Actions

bump imagequant version

Remove dollar signs used before commands without showing output

Use Ubuntu 18.04 in GitHub Actions

Fix Clippy errors and warnings

Use dssim-core to prevent download of unused dependencies

Update dependencies

Update to clap v3

Detail license information in README.md

Use best instead of last attempt from binary search

Move binary search to own function

Refactor test code

Add test for 4:4:4 chroma subsampling (#22)

Add auto chroma subsampling feature (#20)

Allow arbitrary order of ICC markers in JPEG