added env function and test

src/stl.rs

@@ -172,6 +172,17 @@ pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
         },
     );
 
+    syms.insert(
+        "env".to_string(),
+        Symbol {
+            name: String::from("env"),
+            args: Args::None,
+            conditional_branches: false,
+            docs: decl::ENV_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(decl::env_callback)),
+        },
+    );
+
     Ok(())
 }