frost-core: expose SigningKey::to/from_scalar() (#601)

* frost-core: expose SigningKey::to/from_scalar()

* Update frost-core/CHANGELOG.md

frost-core/CHANGELOG.md

@@ -4,6 +4,8 @@ Entries are listed in reverse chronological order.
 
 ## Unreleased
 
+* Exposed the `SigningKey::from_scalar()` and `to_scalar()` methods. This
+  helps interoperability with other implementations.
 
 ## Released
 

frost-core/src/signing_key.rs

@@ -58,7 +58,6 @@ where
     }
 
     /// Creates a SigningKey from a scalar.
-    #[cfg(feature = "internals")]
     pub fn from_scalar(
         scalar: <<<C as Ciphersuite>::Group as Group>::Field as Field>::Scalar,
     ) -> Self {
@@ -66,7 +65,6 @@ where
     }
 
     /// Return the underlying scalar.
-    #[cfg(feature = "internals")]
     pub fn to_scalar(self) -> <<<C as Ciphersuite>::Group as Group>::Field as Field>::Scalar {
         self.scalar
     }