- return true from execute_pipeline if there are any errors
- use todo list to speedup retries
- store initialisation node in CommandsParser object
- add sync context manager for pipeline
- use if/else instead of try/except
- make command a function argument in _determine_nodes & _determine_slot

- add async cluster pipeline benchmark script

* Copy Cluster Client, Commands, Commands Parser, Tests for asyncio

* Async Cluster Tests: Async/Await

* Add Async RedisCluster

* cluster: use ERRORS_ALLOW_RETRY from self.__class__

* async_cluster: rework redis_connection, initialize, & close

- move redis_connection from NodesManager to ClusterNode & handle all related logic in ClusterNode class
- use Locks while initializing or closing
- in case of error, close connections instead of instantly reinitializing
- create ResourceWarning instead of manually deleting client object
- use asyncio.gather to run commands/initialize/close in parallel

- inline single use functions
- fix test_acl_log for py3.6

* async_cluster: add types

* async_cluster: add docs

* docs: update sphinx & add sphinx_autodoc_typehints

* async_cluster: move TargetNodesT to cluster module

* async_cluster/commands: inherit commands from sync class if possible

* async_cluster: add benchmark script with aredis & aioredis-cluster

* async_cluster: remove logging

* async_cluster: inline functions

* async_cluster: manage Connection instead of Redis Client

* async_cluster/commands: optimize parser

* async_cluster: use ensure_future & generators for gather

* async_conn: optimize

* async_cluster: optimize determine_slot

* async_cluster: optimize determine_nodes

* async_cluster/parser: optimize _get_moveable_keys

* async_cluster: inlined check_slots_coverage

* async_cluster: update docstrings

* async_cluster: add concurrent test & use read_response/_update_moved_slots without lock

Co-authored-by: Chayim <chayim@users.noreply.github.com>

@akx Thank you so much for this! Thanks again for introducing me to a new tool that I'm sliding into my workflow as well.  

Remove support for end-of-life Python 2.7

Python 2.7 is end of life. It is no longer receiving bug fixes,
including for security issues. Python 2.7 went EOL on 2020-01-01. For
additional details on support Python versions, see:

Supported: https://devguide.python.org/#status-of-python-branches
EOL: https://devguide.python.org/devcycle/#end-of-life-branches

Removing support for EOL Pythons will reduce testing and maintenance
resources while allowing the library to move towards a modern Python 3
style. Python 2.7 users can continue to use the previous version of
redis-py.

Was able to simplify the code:

- Removed redis._compat module
- Removed __future__ imports
- Removed object from class definition (all classes are new style)
- Removed long (Python 3 unified numeric types)
- Removed deprecated __nonzero__ method
- Use simpler Python 3 super() syntax
- Use unified OSError exception
- Use yield from syntax

Co-authored-by: Andy McCurdy <andy@andymccurdy.com>

flake8 catches a wider net of mistakes than pycodestyle and is more
commonly used by the larger community. For example, it catches unused
imports, a few of which existed. These have since been removed.

Two "noqa" comments were added. One ignores the _compat.py file as it
has a large amount of Python version specific code. The second is in
utils.py which intentionally does not use an import.

Use the "as" keyword to capture the exception in a variable instead of
sys.exc_info().

Re-raise exception with the bare "raise" syntax.

Avoid "# noqa: E722" by catching BaseException, which includes all
exceptions including SystemExit.

Now matches the parent class signature. Running the benchmark previously
failed with the error:

    TypeError: send_packed_command() got an unexpected keyword argument 'check_health'