Merge #390

390: Migrate from deprecated license format to SPDX License Expression r=mkroening a=mkroening

See
https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields https://spdx.dev/spdx-specification-21-web-version/#h.jxpfx0ykyb60



Co-authored-by: Martin Kröning <mkroening@posteo.net>