Improved JSON config error reporting

Show incorrect lines in config.json together with line number and position.

src/base/io/json/Json.h

@@ -28,6 +28,9 @@
 
 #include "base/kernel/interfaces/IJsonReader.h"
 #include "rapidjson/fwd.h"
+#include <string>
+#include <vector>
+#include <fstream>
 
 
 namespace xmrig {
@@ -50,7 +53,12 @@ public:
     static bool get(const char *fileName, rapidjson::Document &doc);
     static bool save(const char *fileName, const rapidjson::Document &doc);
 
+    static bool convertOffset(const char *fileName, size_t offset, size_t &line, size_t &pos, std::vector<std::string>& s);
+
     static rapidjson::Value normalize(double value, bool zero);
+
+private:
+    static bool convertOffset(std::ifstream& ifs, size_t offset, size_t& line, size_t& pos, std::vector<std::string>& s);
 };