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/network/MACAddress.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 MACAddress::MACAddress()
 {
     zeromem (address, sizeof (address));
@@ -71,3 +74,5 @@ bool MACAddress::isNull() const noexcept                                { return
 
 bool MACAddress::operator== (const MACAddress& other) const noexcept    { return memcmp (address, other.address, sizeof (address)) == 0; }
 bool MACAddress::operator!= (const MACAddress& other) const noexcept    { return ! operator== (other); }
+
+}  // namespace beast