Add parser improvements (#2679)

* Add parser improvements

Previously everything starting with "$" was parsed as a column path.
With this commit applied, the lite_arg starting with $ is parsed as
the most appropriate thing
- $true/$false ==> Expression::Boolean
- $(...) ==> Invocation
- $it ==> ColumnPath
- Anything with at least one '.' ==> ColumnPath
- Anything else ==> Variable

* Ignore failing tests

crates/nu-cli/src/evaluate/evaluator.rs

@@ -172,7 +172,7 @@ pub(crate) async fn evaluate_baseline_expr(
 
             Ok(item.value.into_value(tag))
         }
-        Expression::Boolean(_boolean) => unimplemented!(),
+        Expression::Boolean(_boolean) => Ok(UntaggedValue::boolean(*_boolean).into_value(tag)),
         Expression::Garbage => unimplemented!(),
     }
 }