Tidy up includes:

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

beast/unit_test/reporter.h

@@ -22,13 +22,9 @@
 
 #include <beast/unit_test/amount.h>
 #include <beast/unit_test/recorder.h>
-
 #include <beast/streams/abstract_ostream.h>
 #include <beast/streams/basic_std_ostream.h>
-
 #include <boost/optional.hpp>
-#include <boost/ref.hpp>
-
 #include <functional>
 #include <iostream>
 
@@ -116,7 +112,7 @@ public:
     reporter& operator= (reporter const&) = delete;
 
     explicit reporter (std::ostream& stream = std::cout)
-        : m_std_ostream (boost::ref (stream))
+        : m_std_ostream (std::ref (stream))
         , m_stream (*m_std_ostream)
     {
     }