Setup codegen metaprogram skeleton

Going use it to swap macro implementation usage in the compiler.

codegen/gencpp/gen.builder.hpp

@@ -0,0 +1,24 @@
+// This file was generated automatially by gencpp's bootstrap.cpp (See: https://github.com/Ed94/gencpp)
+
+#pragma once
+
+#include "gen.hpp"
+
+GEN_NS_BEGIN
+
+struct Builder
+{
+	FileInfo File;
+	String   Buffer;
+
+	static Builder open( char const* path );
+
+	void pad_lines( s32 num );
+
+	void print( Code );
+	void print_fmt( char const* fmt, ... );
+
+	void write();
+};
+
+GEN_NS_END