Start support for commandline args to nu itself (#851)

* cmdline args wip

* WIP

* redirect working

* Add help and examples

* Only show flags in signature of more than help

crates/nu-parser/src/lib.rs

@@ -12,9 +12,7 @@ pub use flatten::{
 };
 pub use lex::{lex, Token, TokenContents};
 pub use lite_parse::{lite_parse, LiteBlock};
-pub use parse_keywords::{
-    parse_alias, parse_def, parse_def_predecl, parse_let, parse_module, parse_use,
-};
+
 pub use parser::{find_captures_in_expr, parse, trim_quotes, Import};
 
 #[cfg(feature = "plugin")]