Extracted class StringBuilder

JsonGeneratorTests/StringBuilder.cpp

@@ -0,0 +1,14 @@
+#include "StringBuilder.h"
+
+
+void StringBuilder::append(const char* format, ...)
+{
+    char* tail = buffer + length;
+
+    va_list args;
+    va_start(args, format);
+    vsnprintf(tail, capacity - length, format, args);
+    va_end(args);
+
+    length += strlen(tail);
+}