- Backport ResourceTracker from Python 3.8 concurrent.futures and fix
tracker pid issue (204 and 202).
- Fix bug when pickling function with kw-only argument (264).
- Fix bug in `pickler.dispatch_table` handling that could cause a crash
with the new cloudpickle fast pickler under Python 3.8 (203).
- Fix a race condition that could cause a deadlock with PyPy (191).