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/zip/GZIPDecompressorInputStream.cpp

@@ -26,6 +26,9 @@
   ==============================================================================
 */
 
+namespace beast
+{
+
 #if BEAST_MSVC
  #pragma warning (push)
  #pragma warning (disable: 4309 4305 4365)
@@ -290,3 +293,5 @@ unsigned long beast_crc32 (unsigned long crc, const unsigned char* buf, unsigned
 {
     return zlibNamespace::crc32 (crc, buf, len);
 }
+
+}  // namespace beast