Fix API docs to show the correct return type for emplace/insert for multimap and multiset

doc/unordered/unordered_multimap.adoc

@@ -107,17 +107,17 @@ public:
 
   // modifiers
   template<typename... Args>
-  std::pair<iterator, bool>
+  iterator
   emplace(Args&&... args);
 
   template<typename... Args>
   iterator
   emplace_hint(const_iterator hint, Args&&... args);
 
-  std::pair<iterator, bool>
+  iterator
   insert(value_type const& obj);
 
-  std::pair<iterator, bool>
+  iterator
   insert(value_type&& obj);
 
   template <class P>
@@ -715,7 +715,7 @@ Returns:: A `const_iterator` which refers to the past-the-end value for the cont
 ==== emplace
 ```c++
 template<typename... Args>
-std::pair<iterator, bool>
+iterator
 emplace(Args&&... args);
 ```
 
@@ -761,7 +761,7 @@ Since existing `std::pair` implementations don't support `std::piecewise_constru
 
 ==== Copy Insert
 ```c++
-std::pair<iterator, bool>
+iterator
 insert(value_type const& obj);
 ```
 
@@ -779,7 +779,7 @@ Notes:: Can invalidate iterators, but only if the insert causes the load factor
 
 ==== Move Insert
 ```c++
-std::pair<iterator, bool>
+iterator
 insert(value_type&& obj);
 ```
 
@@ -871,10 +871,10 @@ Notes:: The standard is fairly vague on the meaning of the hint. But the only pr
 ```c++
 template <class P>
 iterator
-insert(P&& value);
+insert(const_iterator hint, P&& value);
 ```
 
-Inserts an element into the container by performing `emplace(std::forward<P>(value))`.
+Inserts an element into the container by performing `emplace_hint(hint, std::forward<P>(value))`.
 
 Only participates in overload resolution if `std::is_constructible<value_type, P&&>::value` is `true`.