Release v0.4.0

[natalieesk]

Check version number is correct:

• Frost core version number
• Frost ed25519 version number
• Frost ed448 version number
• Frost p256 version number
• Frost rerandomized version number
• Frost ristretto255 version number
• Frost secp256k1 version number

Update changelog:

• Check content
• Move version in changelog to Released
• Create a new version in “unreleased” in changelog

Update the version number for frost-core in the Ciphersuite crates, e.g. in frost-core = { path = "../frost-core", version = "0.4.0", features = ["test-impl"] }:

• Frost ed25519
• Frost ed448
• Frost p256
• Frost ristretto255
• Frost secp256k1
• Frost rerandomized