Add sha512Half and SHA512HashHasher:

These routines replace existing code to compute SHA512-Half hashes.
The new code accumulates serialized data into a hashing context
instead of allocating a buffer, for improved performance.

src/ripple/app/main/Main.cpp

@@ -19,6 +19,7 @@
 
 #include <BeastConfig.h>
 #include <ripple/basics/Log.h>
+#include <ripple/basics/SHA512Half.h>
 #include <ripple/app/main/Application.h>
 #include <ripple/basics/CheckLibraryVersions.h>
 #include <ripple/basics/StringUtilities.h>
@@ -511,6 +512,10 @@ int main (int argc, char** argv)
     // https://svn.boost.org/trac/boost/ticket/10657
     (void)beast::Time::currentTimeMillis();
 
+#ifdef _MSC_VER
+    ripple::sha512_deprecatedMSVCWorkaround();
+#endif
+
 #if defined(__GNUC__) && !defined(__clang__)
     auto constexpr gccver = (__GNUC__ * 100 * 100) +
                             (__GNUC_MINOR__ * 100) +