Tidy up includes:

* Replace boost with std equivalents:
  - bind, ref, cref, function, placeholders
* More "include what you use"
* Remove unnecessary includes

beast/module/core/logging/Logger.h

@@ -24,6 +24,8 @@
 #ifndef BEAST_LOGGER_H_INCLUDED
 #define BEAST_LOGGER_H_INCLUDED
 
+#include <beast/strings/String.h>
+
 namespace beast
 {