[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/memusage.h

@@ -121,4 +121,4 @@ static inline size_t DynamicUsage(const boost::unordered_map<X, Y, Z>& m)
 
 }
 
-#endif
+#endif // BITCOIN_MEMUSAGE_H