Added backtrace via --trace option and a lot more helpful information for debugging. (0.22.0)

src/vm.h

@@ -66,6 +66,8 @@ typedef struct {
     int current_line; // last executed source line (debug)
 
     int exit_code; // process exit code set by OP_EXIT
+
+    int trace_enabled; // when non-zero, print executed ops and stack
 } VM;
 
 // initialize VM (zero state)