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.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 namespace
 {
     inline size_t bitToIndex (const int bit) noexcept   { return (size_t) (bit >> 5); }
@@ -1014,3 +1017,5 @@ void BigInteger::loadFromMemoryBlock (const MemoryBlock& data)
     for (int i = (int) data.getSize(); --i >= 0;)
         this->setBitRangeAsInt (i << 3, 8, (uint32) data [i]);
 }
+
+}  // namespace beast