General tidy and refactoring:

* Use nullptr (C++11) instead of NULL.
* Put each file into its own namespace declaration.
* Remove "using namespace" directives and add scope qualifiers.
* Control when beast's implementation of std::equal (C++14) is used.
* Tidy up some const declarations.

Conflicts:
	src/ripple_app/shamap/SHAMapSync.cpp
	src/ripple_app/tx/TransactionEngine.cpp

modules/beast_core/misc/Main.cpp

@@ -17,6 +17,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 Main* Main::s_instance;
 
 Main::Main ()
@@ -124,3 +127,5 @@ int Main::runFromMain (int argc, char const* const* argv)
 
     return exitCode;
 }
+
+}  // namespace beast