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/network/Socket.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 #if BEAST_MSVC
  #pragma warning (push)
  #pragma warning (disable : 4127 4389 4018)
@@ -583,3 +586,5 @@ bool DatagramSocket::isLocal() const noexcept
 #if BEAST_MSVC
  #pragma warning (pop)
 #endif
+
+}  // namespace beast