feat: set message for multiple revsets

Allows to set the revision message of multiple revisions by passing
them as arguments. This only supports simple revisions, such as `@`,
`@-`, `xs`, and so on. Comple revisions such as `@..@-` are not
supported.

Fixes: #5

src/jj/mod.rs

@@ -14,7 +14,13 @@ pub trait JjExecutor: Send + Sync {
     async fn is_repository(&self) -> Result<bool, Error>;
 
     /// Set the description of the current change
-    async fn describe(&self, message: &str) -> Result<(), Error>;
+    ///
+    /// The revset parameter should resolve to a single commit (e.g.,
+    /// `"@"`, `"xs"`, bookmark name)
+    async fn describe(&self, revset: &str, message: &str) -> Result<(), Error>;
+
+    /// Get the current description of a specific revision
+    async fn get_description(&self, revset: &str) -> Result<String, Error>;
 }
 
 #[cfg(test)]