Added temp dir for unit test data and cleanup

Unit test data will now go to a temporary dir that will be deleted
once the test completes. The unit tests also setup a logger which
will persist so that it can be inspected once tests complete.

Also fixes a bug where instance var is missing from decode_hybi()

Co-authored-by: natsume.takashi@lab.ntt.co.jp
Merge pull request #105 from dosaboy/topic/unit-test-cleanup

Added temp dir for unit test data and cleanup