Better std::chrono autodetection for Visual Studio

changelog.md

@@ -1,4 +1,5 @@
 HEAD
+- Improvement: Better automatic std::chrono feature detection for Visual Studio
 
 0.6.0
 - MINOR BREAKING TRANSPORT POLICY CHANGE: Custom transport policies will now be

websocketpp/common/chrono.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, Peter Thorson. All rights reserved.
+ * Copyright (c) 2015, Peter Thorson. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -39,6 +39,14 @@
     #endif
 #endif
 
+// If we're on Visual Studio 2012 or higher and haven't explicitly disabled
+// the use of C++11 chrono header then prefer it to boost.
+#if defined(_MSC_VER) && _MSC_VER >= 1700 && !defined _WEBSOCKETPP_NO_CPP11_CHRONO_
+    #ifndef _WEBSOCKETPP_CPP11_CHRONO_
+        #define _WEBSOCKETPP_CPP11_CHRONO_
+    #endif
+#endif
+
 #ifdef _WEBSOCKETPP_CPP11_CHRONO_
     #include <chrono>
 #else