revert sink accepting only char* and size_t

include/spdlog/sinks/base_sink.h

@@ -52,15 +52,15 @@ public:
     base_sink(const base_sink&) = delete;
     base_sink& operator=(const base_sink&) = delete;
 
-    void sink_it(const char* data, size_t size) override
+    void log(const details::log_msg& msg) override
     {
         std::lock_guard<Mutex> lock(_mutex);
-        _sink_it(data, size);
+        _sink_it(msg);
     };
 
 
 protected:
-    virtual void _sink_it(const char* data, size_t size) = 0;
+    virtual void _sink_it(const details::log_msg& msg) = 0;
     Mutex _mutex;
 };
 }