Add GenericValue::ValueType and fix warning for SetString(std::string, Allocator)

include/rapidjson/document.h

@@ -427,6 +427,7 @@ public:
     typedef typename GenericMemberIterator<true,Encoding,Allocator>::Iterator ConstMemberIterator;  //!< Constant member iterator for iterating in object.
     typedef GenericValue* ValueIterator;            //!< Value iterator for iterating in array.
     typedef const GenericValue* ConstValueIterator; //!< Constant value iterator for iterating in array.
+    typedef GenericValue<Encoding, Allocator> ValueType;    //!< Value type of itself.
 
     //!@name Constructors and destructor.
     //@{
@@ -1417,7 +1418,7 @@ public:
         \post IsString() == true && GetString() != s.data() && strcmp(GetString(),s.data() == 0 && GetStringLength() == s.size()
         \note Requires the definition of the preprocessor symbol \ref RAPIDJSON_HAS_STDSTRING.
     */
-    GenericValue& SetString(const std::basic_string<Ch>& s, Allocator& allocator) { return SetString(s.data(), s.size(), allocator); }
+    GenericValue& SetString(const std::basic_string<Ch>& s, Allocator& allocator) { return SetString(s.data(), SizeType(s.size()), allocator); }
 #endif
 
     //@}