Import and export improved

- Import paths are now vname and not sym
- Imports and exports accept multiple space-delimited operators in []

as a result, we can now reliably import and export the operator *

- error reporting ergonomics

src/foreign_macros/define_fn.rs

@@ -41,7 +41,7 @@ use crate::write_fn_step;
 ///
 /// ```
 /// use orchidlang::interpreted::Clause;
-/// use orchidlang::stl::litconv::with_str;
+/// use orchidlang::systems::cast_exprinst::with_str;
 /// use orchidlang::{define_fn, Literal, Primitive};
 ///
 /// define_fn! {expr=x in
@@ -58,7 +58,7 @@ use crate::write_fn_step;
 /// A simpler format is also offered for unary functions:
 ///
 /// ```
-/// use orchidlang::stl::litconv::with_lit;
+/// use orchidlang::systems::cast_exprinst::with_lit;
 /// use orchidlang::{define_fn, Literal};
 ///
 /// define_fn! {