Revert-revert migrate to ed25519-dalek crate (#3877)

* Revert "Revert "Migrate from ring to ed25519-dalek, take 2 (#3844)" (#3868)"

This reverts commit 6a878602f2.

* Fix Signature::verify method

sdk/Cargo.toml

@@ -11,6 +11,7 @@ edition = "2018"
 [dependencies]
 bincode = "1.1.3"
 bs58 = "0.2.0"
+ed25519-dalek = "1.0.0-pre.0"
 hex = "0.3.2"
 byteorder = "1.2.1"
 chrono = { version = "0.4.0", features = ["serde"] }
@@ -18,7 +19,7 @@ generic-array = { version = "0.13.0", default-features = false, features = ["ser
 itertools = "0.8.0"
 log = "0.4.2"
 rand = "0.6.5"
-ring = "0.13.2"
+rayon = "1.0.0"
 sha2 = "0.8.0"
 serde = "1.0.90"
 serde_derive = "1.0.90"