Loky

- Fix interpreter shutdown
- Fix queue size in reusable executor
- Accelerate executor shutdown

- Add documentation, accessible on http://loky.readthedocs.io
- Fixed a thread-safety issue when iterating over the dict of processes in
`ReusablePoolExecutor._resize` and `ProcessPoolExecutor.shutdown`.

- Add `loky.cpu_count` that returns the number of CPUs the current process can
use. This value is now used by default by `ProcessPoolExecutor`. (114).
- Add `__version__` field in the `loky` module (110).
- Fix multiple instabilities and simplify the inner mechanisms (105, 107).

- Fix handling of Full Queue exception at shutdown time. (107).

- Fix a potential deadlock when shutting down a past reusable executor instance
with to create a new instance with different parameters. (101, 102)

- Rename `loky.process_executor.BrokenExecutor` as `loky.BrokenProcessPool` and
subclass `concurrent.futures.process.BrokenProcessPool` when available to make
except statements forward compatible.