Added non const sinks() function to support addition/removal of sinks from existing logger

include/spdlog/details/logger_impl.h

@@ -338,3 +338,8 @@ inline const std::vector<spdlog::sink_ptr> &spdlog::logger::sinks() const
 {
     return sinks_;
 }
+
+inline std::vector<spdlog::sink_ptr> &spdlog::logger::sinks() 
+{
+    return sinks_;
+}

include/spdlog/logger.h

@@ -126,6 +126,8 @@ public:
 
     const std::vector<sink_ptr> &sinks() const;
 
+	std::vector<sink_ptr> &sinks() ;
+
     // error handler
     void set_error_handler(log_err_handler err_handler);
     log_err_handler error_handler();