Misc tasks

[matu3ba]

• [ ] 1. gcc -O3, clang and tcc are not tested
• [ ] 2. you could also use address sanitizer and ub sanitizer (although I would expect they dont find anything)
• [ ] 3. add example usage for multiple types in the README
• [ ] 4. Did you consider using uint8_t instead of int ?
• [x] 5. create a license or SPDX header.