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/Result.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 Result::Result() noexcept {}
 
 Result::Result (const String& message) noexcept
@@ -76,3 +79,5 @@ bool Result::wasOk() const noexcept         { return errorMessage.isEmpty(); }
 Result::operator bool() const noexcept      { return errorMessage.isEmpty(); }
 bool Result::failed() const noexcept        { return errorMessage.isNotEmpty(); }
 bool Result::operator!() const noexcept     { return errorMessage.isNotEmpty(); }
+
+}  // namespace beast