Add language options.

tests/options.rs

@@ -0,0 +1,26 @@
+use rhai::{Engine, EvalAltResult};
+
+#[test]
+fn test_options() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    engine.compile("let x = if y { z } else { w };")?;
+
+    engine.set_allow_if_expression(false);
+
+    assert!(engine.compile("let x = if y { z } else { w };").is_err());
+
+    engine.compile("let x = { let z = 0; z + 1 };")?;
+
+    engine.set_allow_statement_expression(false);
+
+    assert!(engine.compile("let x = { let z = 0; z + 1 };").is_err());
+
+    engine.compile("let x = || 42;")?;
+
+    engine.set_allow_anonymous_fn(false);
+
+    assert!(engine.compile("let x = || 42;").is_err());
+
+    Ok(())
+}