Upgrade to secp256k1 0.5.0

[msgilligan]

secp256k1 0.5.0 has been released.

According to the CHANGELOG:

The ABI is backward compatible with versions 0.4.x and 0.3.x.

So secp256k1-jdk should work with 0.5.0 if it is installed.

I believe the only thing required for us to upgrade our build is to update the README and flake.lock. We should also re-run jextract and generate updated wrapper classes. At some point we will want to add the new secp256k1_ec_pubkey_sort function to our API.

We'll need to wait for secp256k1 0.5.0 to be merged into Nix. There is a PR already: NixOS/nixpkgs#309724

[msgilligan]

0.5.0 is merged into Nix.

• update README.adoc -- PR README: Update to reference secp256k1 0.5.0 #72
• update flake.lock -- PR flake.lock: Update with nix flake update #71
• re-run jextract and generate updated wrapper classes.
• add the new secp256k1_ec_pubkey_sort function to our API.