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/maths/BigInteger.h

@@ -24,6 +24,9 @@
 #ifndef BEAST_BIGINTEGER_H_INCLUDED
 #define BEAST_BIGINTEGER_H_INCLUDED
 
+namespace beast
+{
+
 //==============================================================================
 /**
     An arbitrarily large integer class.
@@ -318,5 +321,6 @@ OutputStream& BEAST_CALLTYPE operator<< (OutputStream& stream, const BigInteger&
  typedef BigInteger BitArray;
 #endif
 
+}  // namespace beast
 
 #endif   // BEAST_BIGINTEGER_H_INCLUDED