start adding error message support

src/err.h

@@ -0,0 +1,7 @@
+#include "returnTypes.h"
+
+extern const ArErr no_err;
+
+ArErr create_err(int64_t line, int64_t column, int length, char *path, const char *type,
+                 const char *fmt, ...);
+void output_err(ArErr err);