Created CopyPair connection set recursive context manager for opening pairs of files. Created DatasetHandle.copy_dataset staticmethod to copy data and potentially compress it at the same time. Created DatasetHandle.copy instancemethod for calling staticmethod Created GroupHandle.copy_group staticmethod for recursive copy with recompression Created GroupHandle.copy instancemethod for calling staticmethod Modified Databse merge, rebase, shard methods to use new backends which support smarter recursion and compression. Legacy merge method left intact.