Separate headers from src and make the headers hpp

Signed-off-by: somebody_master <somebody_master@somebodyserver.mooo.com>

gdextension/include/register_types.hpp

@@ -0,0 +1,16 @@
+/* godot-cpp integration testing project.
+ *
+ * This is free and unencumbered software released into the public domain.
+ */
+
+#ifndef EXAMPLE_REGISTER_TYPES_HPP
+#define EXAMPLE_REGISTER_TYPES_HPP
+
+#include <godot_cpp/core/class_db.hpp>
+
+using namespace godot;
+
+void initialize_test_module(ModuleInitializationLevel p_level);
+void uninitialize_test_module(ModuleInitializationLevel p_level);
+
+#endif // EXAMPLE_REGISTER_TYPES_HPP

gdextension/include/test.hpp

@@ -0,0 +1,17 @@
+#ifndef TEST_HPP
+#define TEST_HPP
+
+#include <godot_cpp/classes/node3d.hpp>
+
+using namespace godot;
+
+class Test : public Node3D {
+	GDCLASS(Test, Node3D);
+
+public:
+	void start_test();
+
+protected:
+	static void _bind_methods();
+};
+#endif