Add helper functions for making shared pointers to rules

- start work on item set class

src/rules/rule.cpp

@@ -0,0 +1,7 @@
+#include "rule.h"
+
+std::ostream& operator<<(std::ostream& stream, const tree_sitter::rules::Rule &rule)
+{
+    stream << rule.to_string();
+    return stream;
+}