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/mod.rs

@@ -0,0 +1,61 @@
+mod append;
+mod autoenv;
+mod autoenv_trust;
+mod autoenv_untrust;
+mod cal;
+mod cd;
+mod compact;
+mod count;
+mod cp;
+mod def;
+mod default;
+mod drop;
+mod each;
+mod echo;
+mod empty;
+mod enter;
+mod every;
+mod first;
+mod flatten;
+mod format;
+mod get;
+mod group_by;
+mod hash_;
+mod headers;
+mod histogram;
+mod insert;
+mod into_int;
+mod keep;
+mod last;
+mod lines;
+mod ls;
+mod math;
+mod merge;
+mod mkdir;
+mod move_;
+mod open;
+mod parse;
+mod path;
+mod prepend;
+mod random;
+mod range;
+mod reduce;
+mod rename;
+mod reverse;
+mod rm;
+mod save;
+mod select;
+mod semicolon;
+mod skip;
+mod sort_by;
+mod split_by;
+mod split_column;
+mod split_row;
+mod str_;
+mod touch;
+mod uniq;
+mod update;
+mod where_;
+mod which;
+mod with_env;
+mod wrap;