Loky

- 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).

- Fixed loky pickler in workers. (184)

- Fixed compat with python2.7 in semaphore tracker. (186)

- Fixed a bug when setting the cause of an exception without message
under Python 2.7 (179).

- Default serialization is now done with `cloudpickle`. (178)

- The base `Pickler` in `loky` can now be changed through the `LOKY_PICKLER`
variable or programmatically with `set_loky_pickler`. (171)

- Improve reporting of causes in python2.7 (174)

- Improve workers crash reporting by displaying the exitcodes of
workers in `TerminatedWorkerError` (173)

- Add a `wrap_non_picklable_objects` decorator in `loky` to make it
easy to fix serialization failure for nested functions defined in
the `__main__` module. (171)

- Improve error reporting when a worker process is terminated abruptly
(169).

- Remove spurious debug output.

- Add support for PyPy3.

- `loky.cpu_count()` is now upper-bounded by the value of the
`LOKY_MAX_CPU_COUNT` environment variable (when defined).

- Fix issue 165 to make `loky.cpu_count()` return an integer under
Python 2.7 with fractional docker CPU usage quotas.