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/streams/MemoryOutputStream.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 MemoryOutputStream::MemoryOutputStream (const size_t initialSize)
   : blockToUse (&internalBlock), externalData (nullptr),
     position (0), size (0), availableSize (0)
@@ -206,4 +209,6 @@ OutputStream& BEAST_CALLTYPE operator<< (OutputStream& stream, const MemoryOutpu
         stream.write (streamToRead.getData(), dataSize);
 
     return stream;
-}
+}
+
+}  // namespace beast