Just a tip. Yes, Pugi is only an XML parsing library, but that is pretty much all you need (my opinon - others may vary). I guess one could go with tinyXML2 too. The ones refed just struck me as having both zlib + bsd license and extra dependencies (ex zlib and tinyXML) that seems a bit unnecessary to do such a simple task.
I entirely agree that an XML parsing library is usually all you need, and of course it has the added benefit that you don't depend on a 3rd party software package to get updated when something new is added to the TMX map format. Maybe it's worth adding a note about this to the documentation.