Code cleanup

• Add SPDX license identifiers to files
  • src/example/ was not modified because it does not declare a license
• Update Rust edition from 2015 to 2018
• Fix or silence clippy warnings
• Add wasm32 target to CI to ensure it continues to build
• Mark color::Color as transparent rather than packed

added 3 commits

• 5569f2e2 - CI: Add wasm32 target
• 08ac423a - Fix or silence clippy warnings
• 58ed34c7 - color: Use repr transparent instead of packed

Compare with previous version

merged

mentioned in commit 152c913f