message: Clarify K/V purge documentation verbiage
diff: @@ -543,7 +543,7 @@ impl Store {
  Ok(())
  }
  - /// Purges the given key, destructively removing everything from the bucket.
  + /// Purges all the revisions of a entry destructively, leaving behind a single purge entry in-place.
  ///
  /// # Examples
  ///
  