Print error messages to stderr (instead of stdout).

src/mathlib.cpp

@@ -216,7 +216,7 @@ std::string MathLib::calculate(const std::string &first, const std::string &seco
         break;
 
     default:
-        std::cout << "##### If you see this, there is a bug: "
+        std::cerr << "##### If you see this, there is a bug: "
                   << "MathLib::calculate() was called with unknown action '"
                   << action
                   << "' #####"

src/token.cpp

@@ -385,7 +385,7 @@ bool Token::Match(const Token *tok, const char pattern[], unsigned int varid)
             {
                 if (varid == 0)
                 {
-                    std::cout << "\n###### If you see this, there is a bug ###### Token::Match() - varid was 0" << std::endl;
+                    std::cerr << "\n###### If you see this, there is a bug ###### Token::Match() - varid was 0" << std::endl;
                 }
 
                 if (tok->varId() != varid)

src/tokenize.cpp

@@ -3503,7 +3503,7 @@ void Tokenizer::syntaxError(const Token *tok, char c)
 
     if (!_errorLogger)
     {
-        std::cout << "### Unlogged error at Tokenizer::syntaxError: Invalid number of character ("
+        std::cerr << "### Unlogged error at Tokenizer::syntaxError: Invalid number of character ("
                   << c << ")"
                   << std::endl;
         return;