[Trivial] ensure minimal header conventions

- ensure header namespaces and end comments are correct
- add missing header end comments
- ensure minimal formatting (add newlines etc.)

src/bench/bench.cpp

@@ -1,7 +1,9 @@
 // Copyright (c) 2015 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #include "bench.h"
+
 #include <iostream>
 #include <sys/time.h>