* Implement basic tree hash caching
* Use spaces to indent top-level Cargo.toml
* Optimize BLS tree hash by hashing bytes directly
* Implement tree hash caching for validator registry
* Persist BeaconState tree hash cache to disk
* Address Paul's review comments
* 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
