Publish ssz_types (and deps) to crates.io (#468)

* Rename `hashing` crate to `eth2_hashing`

* Add license, desc to eth2_hashing Cargo.toml

* Remove merkle root from eth2 hashing

* Remove old benches folder (zombied from old branch)

* Add docs to eth2_hashing

* Prepare tree_hash for publishing on crates.io

* Update deps to use crates.io instead of paths

* Update all crates to pull ssz from crates.io

* Remove cached_tree_hash, add patches to manifest

* Fix compile error in benches

* Remove unused code

* Fix fake_crypto compile error

eth2/utils/eth2_hashing/src/lib.rs

@@ -0,0 +1,44 @@
+//! Provides a simple hash function utilizing `ring::digest::SHA256`.
+//!
+//! The purpose of this crate is to provide an abstraction to whatever hash function Ethereum
+//! 2.0 is using. The hash function has been subject to change during the specification process, so
+//! defining it once in this crate makes it easy to replace.
+
+#[cfg(not(target_arch = "wasm32"))]
+use ring::digest::{digest, SHA256};
+
+#[cfg(target_arch = "wasm32")]
+use sha2::{Digest, Sha256};
+
+/// Returns the digest of `input`.
+///
+/// Uses `ring::digest::SHA256`.
+pub fn hash(input: &[u8]) -> Vec<u8> {
+    #[cfg(not(target_arch = "wasm32"))]
+    let h = digest(&SHA256, input).as_ref().into();
+
+    #[cfg(target_arch = "wasm32")]
+    let h = Sha256::digest(input).as_ref().into();
+
+    h
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rustc_hex::FromHex;
+
+    #[cfg(target_arch = "wasm32")]
+    use wasm_bindgen_test::*;
+
+    #[cfg_attr(not(target_arch = "wasm32"), test)]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+    fn test_hashing() {
+        let input: Vec<u8> = b"hello world".as_ref().into();
+
+        let output = hash(input.as_ref());
+        let expected_hex = "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9";
+        let expected: Vec<u8> = expected_hex.from_hex().unwrap();
+        assert_eq!(expected, output);
+    }
+}