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/threads/HighResolutionTimer.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 HighResolutionTimer::HighResolutionTimer()                    { pimpl = new Pimpl (*this); }
 HighResolutionTimer::~HighResolutionTimer()                   { stopTimer(); }
 
@@ -29,3 +32,5 @@ void HighResolutionTimer::stopTimer()                         { pimpl->stop(); }
 
 bool HighResolutionTimer::isTimerRunning() const noexcept     { return pimpl->periodMs != 0; }
 int HighResolutionTimer::getTimerInterval() const noexcept    { return pimpl->periodMs; }
+
+}  // namespace beast