v0.5.0 release

This release includes the following new features and improvements:

Support MuSig2*

MuSig2* as defined in BIP-327 is now supported.

require 'schnorr'

sk1 = 1 + SecureRandom.random_number(Schnorr::GROUP.order - 1)
pk1 = (Schnorr::GROUP.generator.to_jacobian * sk1).to_affine.encode

sk2 = 1 + SecureRandom.random_number(Schnorr::GROUP.order - 1)
pk2 = (Schnorr::GROUP.generator.to_jacobian * sk2).to_affine.encode

pubkeys = [pk1, pk2]

# Key aggregation.
agg_ctx = Schnorr::MuSig2.aggregate(pubkeys)
# if you have tweak value.
agg_ctx = Schnorr::MuSig2.aggregate_with_tweaks(pubkeys, tweaks, modes)

## Aggregated pubkey is
### Return point:
agg_ctx.q
### Return x-only pubkey string
agg_ctx.x_only_pubkey

msg = SecureRandom.bytes(32)

# Generate secret nonce and public nonce.
sec_nonce1, pub_nonce1 = Schnorr::MuSig2.gen_nonce(
        pk: pk1,
        sk: sk1,  # optional
        agg_pubkey: agg_ctx.x_only_pubkey,  # optional
        msg: msg, # optional
        extra_in: SecureRandom.bytes(4),  # optional
        rand: SecureRandom.bytes(32)  # optional
)

## for stateless signer.
agg_other_nonce = described_class.aggregate_nonce([pub_nonce1])
pub_nonce2, sig2 = described_class.deterministic_sign(
        sk2, agg_other_nonce, pubkeys, msg, 
        tweaks: tweaks, # optional
        modes: modes, # optional
        rand: SecureRandom.bytes(32)  # optional
)

# Nonce aggregation
agg_nonce = Schnorr::MuSig2.aggregate_nonce([pub_nonce1, pub_nonce2])

# Generate partial signature.
session_ctx = Schnorr::MuSig2::SessionContext.new(
        agg_nonce, pubkeys, msg, 
        tweaks, # optional
        modes # optional
)
sig1 = session_ctx.sign(sec_nonce1, sk1)

# Verify partial signature.
signer_index = 0
session_ctx.valid_partial_sig?(sig1, pub_nonce1, signer_index)

# Signature aggregation.
sig = session_ctx.aggregate_partial_sigs([sig1, sig2])

# Verify signature.
Schnorr.valid_sig?(msg, agg_ctx.x_only_pubkey, sig.encode)

Performance improvement

Performance has been improved by performing elliptic curve operations in Jacobian coordinates using the ecdsa_ext gem.

Full Changelog: v0.4.0...v0.5.0