Decide the features we want to have

[TimoGlastra]

Rust allows us to expose "features". With these features we can tell the compiler to only compile a part of the complete library. This might be useful in mobile scenarios as we might only care about the holder functionality.

First we would need to determine whether we want features, and which specifically.

Some examples are; holder, verifier, issuer, revocation, WASM, FFI, vendored, logger, specific crypto suites, etc.

For now we current features will suffice, but it might be worthwhile investigating whether the library will shrink in size when it is only built for a holder with FFI.