Use version preprocessor guards for RocksDB unique_ptr API, retain unique_ptr internally

src/ifcparse/storage.h

@@ -31,6 +31,7 @@ namespace rocksdb {
 #include <iostream>
 #include <vector>
 #include <list>
+#include <memory>
 
 #ifndef SWIG
 
@@ -308,7 +309,7 @@ namespace IfcParse {
 
         class IFC_PARSE_API rocks_db_file_storage {
         public:
-            rocksdb::DB* db;
+            std::unique_ptr<rocksdb::DB> db;
             rocksdb::WriteOptions wopts;
             rocksdb::ReadOptions ropts;
             IfcParse::IfcFile* file;