usql update

usql/exception.h

@@ -1,14 +1,12 @@
 #pragma once
 
-#include "lexer.h"
-
 #include <string>
 
 namespace usql {
 
 class Exception : public std::runtime_error {
 public:
-    Exception(const std::string msg);
+    explicit Exception(std::string msg);
 };
 
 }	// namespace