Implemented P0084R2 (Emplace Return Type)

include/boost/container/static_vector.hpp

@@ -677,6 +677,8 @@ public:
     //! @brief Inserts a Value constructed with
     //!   \c std::forward<Args>(args)... in the end of the container.
     //!
+    //! @return A reference to the created object.
+    //!
     //! @param args     The arguments of the constructor of the new element which will be created at the end of the container.
     //!
     //! @par Throws
@@ -685,7 +687,7 @@ public:
     //! @par Complexity
     //!   Constant O(1).
     template<class ...Args>
-    void emplace_back(Args &&...args);
+    reference emplace_back(Args &&...args);
 
     //! @pre
     //!  @li \c p must be a valid iterator of \c *this in range <tt>[begin(), end()]</tt>