Replaced the queue of Token pointers with values.

We were getting memory leaks (as told by the CRT detectors, which I also added), and there's really no reason (as long as we're careful) to use pointers there.

include/exceptions.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <exception>
+#include <string>
 
 namespace YAML
 {
@@ -9,6 +10,7 @@ namespace YAML
 	public:
 		ParserException(int line_, int column_, const std::string& msg_)
 			: line(line_), column(column_), msg(msg_) {}
+
 		int line, column;
 		std::string msg;
 	};