refactor: prepare for library split

src/main.zig

@@ -130,7 +130,7 @@ fn render_file(a: std.mem.Allocator, writer: anytype, content: []const u8, file_
         }
     };
     var ctx: Ctx = .{ .writer = writer, .content = content, .theme = theme };
-    try parser.render(&ctx, Ctx.cb);
+    try parser.render(&ctx, Ctx.cb, null);
     try ctx.writer.writeAll(content[ctx.last_pos..]);
 }