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converted to esm module, cjs backwards compatible using rollup

• don't support mixing casing for r,g,b properties, either all upper or all lower
• use camelCase instead of snake_case
• snake_case -> camelCase mappings are still present to not break more dependents than necessary.
• fixed jsdoc types and type checking using tsc
• only run tests on node > 18
• no more travis, use github actions
• bumped all deps
• added linting

Allow lowercase r, g, b in RGB object.

Performance improvements and expose raw Lab functions for better performance.