Initial commit

Combines the existing frost-rs, dalek-ff-group, and monero-rs repos into 
a monorepo. Makes tweaks necessary as needed. Replaces RedDSA (which was 
going to be stubbed out into a new folder for now) with an offset system 
that voids its need and allows stealth addresses with CLSAG.

sign/monero/tests/key_image.rs

@@ -0,0 +1,36 @@
+#![cfg(feature = "multisig")]
+
+use rand::rngs::OsRng;
+
+use monero_sign::{SignError, key_image};
+
+mod frost;
+use crate::frost::generate_keys;
+
+#[test]
+fn test() -> Result<(), SignError> {
+  let (keys, group_private) = generate_keys(3, 5);
+  let image = key_image::single(&group_private);
+
+  let mut packages = vec![];
+  packages.resize(5 + 1, None);
+  let included = vec![1, 3, 4];
+  for i in &included {
+    let i = *i;
+    packages[i] = Some(
+      (
+        keys[0].verification_shares()[i].0,
+        key_image::multisig(&mut OsRng, &keys[i - 1], &included)
+      )
+    );
+  }
+
+  for i in included {
+    let mut packages = packages.clone();
+    packages.push(None);
+    let package = packages.swap_remove(i).unwrap().1;
+    assert_eq!(image, package.resolve(packages).unwrap());
+  }
+
+  Ok(())
+}