The crypto::x25519 module provides functions to generate key pairs and to
derive shared keys between them, based on curve25519.

A key pair is created by generating a private key with [[newkey]] and deriving
the public key with [[pubkey]]. A shared key can be found by using [[derive]].

Do not use the same secret key for both key exchanges and signatures. The public
keys are different and revealing both may leak information.

This is a low-level module which implements cryptographic primitives. Direct use
of cryptographic primitives is not recommended for non-experts, as incorrect use
of these primitives can easily lead to the introduction of security
vulnerabilities. Non-experts are advised to use the high-level operations
available in the top-level [[crypto::]] module.

Be advised that Hare's cryptography implementations have not been audited.
