Move debug output from cout to cerr not to mess up generated HTML

debug.cpp

@@ -10,7 +10,7 @@ Debug::Debug(int n) : lvl(n) {
 
 		indent.append(lvl - 1, '\t');
 		if (lvl > 1) indent.append("*** ");
-		std::cout << indent;
+		std::cerr << indent;
 
 // 		std::time_t now = std::time(nullptr);
 // 		std::string dt = std::ctime(&now);
@@ -19,7 +19,7 @@ Debug::Debug(int n) : lvl(n) {
 }
 
 Debug::~Debug() {
-	if (lvl <= debug_level) std::cout << '\n';
+	if (lvl <= debug_level) std::cerr << '\n';
 }
 
 void Debug::set_debug_level(int n) { debug_level = n; }