Move most of the root package into a subcrate. (#1445)

This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).

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

@@ -0,0 +1,97 @@
+use nu_test_support::fs::Stub::FileWithContentToBeTrimmed;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, nu_error, pipeline};
+
+#[test]
+fn changes_the_column_name() {
+    Playground::setup("rename_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "los_cuatro_mosqueteros.txt",
+            r#"
+                Andrés N. Robalino
+                Jonathan Turner
+                Yehuda Katz
+                Jason Gedge
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open los_cuatro_mosqueteros.txt
+                | lines
+                | wrap name
+                | rename mosqueteros
+                | get mosqueteros
+                | count
+                | echo $it
+                "#
+        ));
+
+        assert_eq!(actual, "4");
+    })
+}
+
+#[test]
+fn keeps_remaining_original_names_given_less_new_names_than_total_original_names() {
+    Playground::setup("rename_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "los_cuatro_mosqueteros.txt",
+            r#"
+                Andrés N. Robalino
+                Jonathan Turner
+                Yehuda Katz
+                Jason Gedge
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open los_cuatro_mosqueteros.txt
+                | lines
+                | wrap name
+                | default hit "arepa!"
+                | rename mosqueteros
+                | get hit
+                | count
+                | echo $it
+                "#
+        ));
+
+        assert_eq!(actual, "4");
+    })
+}
+
+#[test]
+fn errors_if_no_columns_present() {
+    Playground::setup("rename_test_3", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "los_cuatro_mosqueteros.txt",
+            r#"
+                Andrés N. Robalino
+                Jonathan Turner
+                Yehuda Katz
+                Jason Gedge
+            "#,
+        )]);
+
+        let actual = nu_error!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open los_cuatro_mosqueteros.txt
+                | lines
+                | rename mosqueteros
+                "#
+        ));
+
+        assert!(
+            actual.contains("no column names available"),
+            format!("actual: {:?}", actual)
+        );
+        assert!(
+            actual.contains("can't rename"),
+            format!("actual: {:?}", actual)
+        );
+    })
+}