Merge rust-bitcoin#4919: Add a sha3_256 module with SHA3-256

5524934 Add a unit test for `sha3` (rustaceanrob)
5fa8a5d Add the SHA3-256 hash function (rustaceanrob)

Pull request description:

  My first commit message motivates this change. The brief explanation is Tor nodes are advertised by ED25519 public key, but are often discoverable as `.onion` addresses. To go from public key to onion address, one must take `SHA3(".onion checksum" | PUBKEY | VERSION)` for a checksum. I will leave the rest for the commit message, as well as all reference material.


ACKs for top commit:
  tcharding:
    ACK 5524934
  apoelstra:
    ACK 5524934; successfully ran local tests


Tree-SHA512: 36f4fdc58bf4a87370a4f3623c3c0d83f414e7e3acccb063e59abe5556b43d5f0dfbe977db3bc88948ee4f65f8b28eef13ebd35ba6a9114fa1ed15ef2fd7eb28

Author: apoelstra

hashes/src/lib.rs

@@ -116,6 +116,7 @@ pub mod sha384;
 pub mod sha512;
 pub mod sha512_256;
 pub mod siphash24;
+pub mod sha3_256;
 
 use core::fmt::{self, Write as _};
 use core::{convert, hash};
@@ -153,6 +154,8 @@ pub use sha512_256::Hash as Sha512_256;
 /// SipHash-2-4: Alias for the [`siphash24::Hash`] hash type.
 #[doc(inline)]
 pub use siphash24::Hash as Siphash24;
+/// SHA3-256: Alias for the [`sha3_256::Hash`] hash type.
+pub use sha3_256::Hash as Sha3_256;
 
 /// Attempted to create a hash from an invalid length slice.
 #[deprecated(since = "TBD", note = "unused now that `Hash::from_slice` is deprecated")]