#include "tmx\MapLoader.h"
...
tmx::MapLoader ml("testmap\\intromap");
...
Don't use backslashes ('
\')in paths. Just use frontslashes ('
/') since they A) work on all platforms (yes, even Windows) and B) You don't need to escape them with an extra backslash. Just get into the habit now and then be happy when you need to port your code to a different platform in the future.
Anyway. You are having linker problems about unresolved symbols.
That usually means that you forgot to link a library that you use or linked the libraries in the wrong order.
The library in question seem to be PugiXML, so make sure you are linking that to your project.