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/empty.rs

@@ -0,0 +1,86 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn reports_emptiness() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [[are_empty];
+                     [$(= [[check]; [[]]      ])]
+                     [$(= [[check]; [""]      ])]
+                     [$(= [[check]; [$(wrap)] ])]
+            ]
+            | get are_empty
+            | empty? check
+            | where check
+            | count
+        "#
+    ));
+
+    assert_eq!(actual.out, "3");
+}
+
+#[test]
+fn sets_block_run_value_for_an_empty_column() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [
+                     [  first_name, last_name,   rusty_at, likes  ];
+                     [      Andrés,  Robalino, 10/11/2013,   1    ]
+                     [    Jonathan,    Turner, 10/12/2013,   1    ]
+                     [       Jason,     Gedge, 10/11/2013,   1    ]
+                     [      Yehuda,      Katz, 10/11/2013,  ''    ]
+            ]
+            | empty? likes { = 1 }
+            | get likes
+            | math sum
+        "#
+    ));
+
+    assert_eq!(actual.out, "4");
+}
+
+#[test]
+fn sets_block_run_value_for_many_empty_columns() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [
+                     [  boost   check   ];
+                     [     1,    []     ]
+                     [     1,    ""     ]
+                     [     1,  $(wrap)  ]
+            ]
+            | empty? boost check { = 1 }
+            | get boost check
+            | math sum
+        "#
+    ));
+
+    assert_eq!(actual.out, "6");
+}
+
+#[test]
+fn passing_a_block_will_set_contents_on_empty_cells_and_leave_non_empty_ones_untouched() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+            echo [
+                     [      NAME, LVL,   HP ];
+                     [    Andrés,  30, 3000 ]
+                     [  Alistair,  29, 2900 ]
+                     [    Arepas,  "",   "" ]
+                     [     Jorge,  30, 3000 ]
+            ]
+            | empty? LVL { = 9 }
+            | empty? HP {
+                = $it.LVL * 1000
+              }
+            | math sum
+            | get HP
+        "#
+    ));
+
+    assert_eq!(actual.out, "17900");
+}