Implement duk_is_error.

src/lib.rs

@@ -38,6 +38,14 @@ extern "C" {
         message: *const i8) -> duk_idx_t;
 }
 
+extern "C" {
+    /// Returns 1 if value at idx inherits from Error, otherwise returns 0. If idx is invalid, also returns 0.
+    pub fn duk_is_error(
+        ctx: *mut duk_context,
+        idx: duk_idx_t
+    ) -> duk_bool_t;
+}
+
 #[cfg(test)]
 mod tests {
     #[test]