nu-cli refactor moving commands into their own crate nu-command (#2910)

* move commands, futures.rs, script.rs, utils

* move over maybe_print_errors

* add nu_command crate references to nu_cli

* in commands.rs open up to pub mod from pub(crate)

* nu-cli, nu-command, and nu tests are now passing

* cargo fmt

* clean up nu-cli/src/prelude.rs

* code cleanup

* for some reason lex.rs was not formatted, may be causing my error

* remove mod completion from lib.rs which was not being used along with quickcheck macros

* add in allow unused imports

* comment out one failing external test; comment out one failing internal test

* revert commenting out failing tests; something else might be going on; someone with a windows machine should check and see what is going on with these failing windows tests

* Update Cargo.toml

Extend the optional features to nu-command

Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>

crates/nu-command/tests/commands/save.rs

@@ -0,0 +1,49 @@
+use nu_test_support::fs::{file_contents, Stub::FileWithContent};
+use nu_test_support::nu;
+use nu_test_support::playground::Playground;
+
+#[test]
+fn figures_out_intelligently_where_to_write_out_with_metadata() {
+    Playground::setup("save_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContent(
+            "cargo_sample.toml",
+            r#"
+                [package]
+                name = "nu"
+                version = "0.1.1"
+                authors = ["Yehuda Katz <wycats@gmail.com>"]
+                description = "A shell for the GitHub era"
+                license = "ISC"
+                edition = "2018"
+            "#,
+        )]);
+
+        let subject_file = dirs.test().join("cargo_sample.toml");
+
+        nu!(
+            cwd: dirs.root(),
+            "open save_test_1/cargo_sample.toml | save"
+        );
+
+        let actual = file_contents(&subject_file);
+        assert!(actual.contains("0.1.1"));
+    })
+}
+
+#[test]
+fn writes_out_csv() {
+    Playground::setup("save_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![]);
+
+        let expected_file = dirs.test().join("cargo_sample.csv");
+
+        nu!(
+            cwd: dirs.root(),
+            r#"echo [[name, version, description, license, edition]; [nu, "0.14", "A new type of shell", "MIT", "2018"]] | save save_test_2/cargo_sample.csv"#,
+        );
+
+        let actual = file_contents(expected_file);
+        println!("{}", actual);
+        assert!(actual.contains("nu,0.14,A new type of shell,MIT,2018"));
+    })
+}