Wrote this to find what turned out to be an external error when
using the interfacing programs, but felt like it might as well be added.

Under the same key and message, the signature is expected to be identical.
However, as the index changes, this case will not happen in real use.

This makes it easier to mix and match with other implementations
for compatibility testing.

Previously this was generated and thus gitignored

This starts a cleanup / refactor, but there is still some low-hanging fruit.