added missing exists() method in C++ database

include/sdskv-client.hpp

@@ -1305,6 +1305,14 @@ class database {
         return m_ph.m_client->get(*this, std::forward<T>(args)...);
     }
 
+    /**
+     * @brief @see client::exists
+     */
+    template<typename ... T>
+    decltype(auto) exists(T&& ... args) const {
+        return m_ph.m_client->exists(*this, std::forward<T>(args)...);
+    }
+
     /**
      * @brief @see client::erase.
      */