Add subcommands. Switch from-* and to-* to them (#1708)

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

@@ -4,7 +4,7 @@ use nu_test_support::nu;
 fn drop_rows() {
     let actual = nu!(
         cwd: "tests/fixtures/formats",
-        r#"echo '[{"foo": 3}, {"foo": 8}, {"foo": 4}]' | from-json | drop 2 | get foo | sum | echo $it"#
+        r#"echo '[{"foo": 3}, {"foo": 8}, {"foo": 4}]' | from json | drop 2 | get foo | sum | echo $it"#
     );
 
     assert_eq!(actual, "3");