Option to replace command same name (#374)

* option to replace command same name

* moved order of custom value declarations

* arranged dataframe folders and objects

* sort help commands by name

* added dtypes function for debugging

* corrected name for dataframe commands

* command names using function

crates/nu-protocol/src/lib.rs

@@ -26,7 +26,5 @@ pub use signature::*;
 pub use span::*;
 pub use syntax_shape::*;
 pub use ty::*;
-pub use value::*;
-
-#[cfg(feature = "custom")]
 pub use value::CustomValue;
+pub use value::*;