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/range.rs

@@ -0,0 +1,47 @@
+use nu_test_support::fs::Stub::EmptyFile;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn selects_a_row() {
+    Playground::setup("range_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![EmptyFile("notes.txt"), EmptyFile("tests.txt")]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls
+                | sort-by name
+                | range 0..0
+                | get name
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "notes.txt");
+    });
+}
+
+#[test]
+fn selects_some_rows() {
+    Playground::setup("range_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("notes.txt"),
+            EmptyFile("tests.txt"),
+            EmptyFile("persons.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls
+                | get name
+                | range 1..2
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "2");
+    });
+}