adding digest helper utility

include/fc/crypto/digest.hpp

@@ -0,0 +1,15 @@
+#pragma once
+#include <fc/io/raw.hpp>
+#include <fc/reflect/reflect.hpp>
+#include <fc/crypto/sha256.hpp>
+
+namespace fc {
+
+   template<typename T>
+   fc::sha256 digest( const T& value )
+   {
+      fc::sha256::encoder enc;
+      fc::raw::pack( enc, value );
+      return enc.result();
+   }
+}