Log Message:
ocaml-optint: update to 0.1.0.

### v0.1.0 2021-03-30 Paris (France)

- Annotate integer types with `[@@immediate64]` (@CraigFe, #13)
- Move unwrapped module `Int63` to `Optint.Int63` (@CraigFe, #13)

### v0.0.5 2021-02-22 Paris (France)

- Update the README.md (@CraigFe, #9)
- Add a representation of 63-bit integers (@CraigFe, #9)
- Allow to compile fuzzers on 32-bit architectures (@dinosaure, #9)
- Add encode / decode functions for integers (@CraigFe, #9)
- Fix `optint` about sign and cast on all architectures (@dinosaure, #9)
- **breaking changes**, rename and handle properly sign-bit:
  `{of,to}_int` become `{of,to}_unsigned_int`
  `{of,to}_int32` become `{of,to}_unsigned_int32`
  Previous functions handle sign-bit correctly