Separate RNG library (#470)

* seperates the RNG library

* fixes crypto tests

* adds rng256 workflow

* fixes formatting

libraries/rng256/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "rng256"
+version = "0.1.0"
+authors = [
+  "Fabian Kaczmarczyck <kaczmarczyck@google.com>",
+  "Guillaume Endignoux <guillaumee@google.com>",
+  "Jean-Michel Picod <jmichel@google.com>",
+]
+license = "Apache-2.0"
+edition = "2018"
+
+[dependencies]
+libtock_drivers = { path = "../../third_party/libtock-drivers" }
+arrayref = "0.3.6"
+rand = { version = "0.6.5", optional = true }
+
+[features]
+std = ["rand"]