Add support for json file signing

Switch from portbase to structures lib, update build and version system

Bump version

Bump version

Bump version

Bump version

Merge pull request #8 from safing/fix/slice-space

Copy input data if slice has additional space

Merge pull request #7 from safing/feature/labeled-hash-formats

Switch to explicit labeled hash formatting, update deps and docs

Merge pull request #5 from safing/fix/compatibility-and-checks

Fix compatibility and checks

Bump version to 0.2