Aliases (#1589)

* WIP getting scopes right

* finish adding initial support

* Finish with alias and add startup commands

crates/nu-cli/tests/commands/alias.rs

@@ -0,0 +1,17 @@
+use nu_test_support::nu;
+use nu_test_support::playground::Playground;
+
+#[test]
+fn alias_args_work() {
+    Playground::setup("append_test_1", |dirs, _| {
+        let actual = nu!(
+            cwd: dirs.root(),
+            r#"
+                alias double_echo [a b] {echo $a $b}
+                double_echo 1 2 | to-json
+            "#
+        );
+
+        assert_eq!(actual, "[1,2]");
+    })
+}

crates/nu-cli/tests/commands/mod.rs

@@ -1,3 +1,4 @@
+mod alias;
 mod append;
 mod calc;
 mod cd;