feat: or keyword (#315)

Add `or` operator to Rego languages. Available via `rego-extensions`
Cargo feature.

If the evaluated lhs value is not false, null or undefined it is returned.
Otherwise rhs is evaluated and returned.

or operator has least precedence, and is left-associative.

closes #314

src/tests/interpreter/mod.rs

@@ -385,6 +385,11 @@ fn yaml_test_impl(file: &str) -> Result<()> {
 }
 
 fn yaml_test(file: &str) -> Result<()> {
+    #[cfg(not(feature = "rego-extensions"))]
+    if file.contains("rego-extensions") {
+        return Ok(());
+    }
+
     match yaml_test_impl(file) {
         Ok(_) => Ok(()),
         Err(e) => {