Error Messaging Redesign

This commit contains the following:

* New data types to support full tracebacks
* New traceback data type used across stl and ast
* Updates to tests
* fixes for error messaging in sym and some stl functions

tests/test_lib_decl.rs

@@ -80,8 +80,8 @@ mod decl_lib_tests {
         let eval_result = eval(&lex(&doc3.to_string()).unwrap(), &mut syms);
         if let Err(s) = eval_result {
             assert_eq!(
-                s.to_string(),
-                "error in call to test: undefined symbol: test".to_string()
+                s.0.first().unwrap().message,
+                "(is an undefined symbol)".to_string()
             );
         } else {
             assert!(false);