- various engine updates from Raze.

* removed refreshFreq variable and related code. This only got into the backend because of stupid interpolation code in some of the Build games which has long been removed.
* save FixedBitArrays as base64 in savegames.
* allow indirections in the string table - by prefixing the language string with '$$' the remaining text is interpreted as another string label to resolve.
* constexpr in palette code, also replacing #defines with enums.

src/common/engine/serializer.cpp

@@ -54,6 +54,7 @@
 #include "engineerrors.h"
 #include "textures.h"
 #include "texturemanager.h"
+#include "base64.h"
 
 extern DObject *WP_NOCHANGE;
 bool save_full = false;	// for testing. Should be removed afterward.
@@ -772,6 +773,31 @@ error:
 	return buff;
 }
 
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+FSerializer &FSerializer::SerializeMemory(const char *key, void* mem, size_t length)
+{
+	if (isWriting())
+	{
+		auto array = base64_encode((const uint8_t*)mem, length);
+		AddString(key, (const char*)array.Data());
+	}
+	else
+	{
+		auto cp = GetString(key);
+		if (key)
+		{
+			base64_decode(mem, length, cp);
+		}
+	}
+	return *this;
+}
+
+
 //==========================================================================
 //
 //