Co-authored-by: Chayim <chayim@users.noreply.github.com>
Co-authored-by: Anas <anas.el.amraoui@live.com>

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>

Prior to this, escaped slashes ("\\") were un-escaped. This caused the strings
"foo\x92" and "foo\\x92" to be represented the same way in the output.

Fixes #1349

Fix test suite with Redis versions pre-5.0.0

The client section of MONITOR output varies for TCP connections, unix socket
connections and commands executed from Lua scripts. Account for each of these
cases by including an additional key `client_type` in the MONITOR output.
`client_type` will be one of ('tcp', 'unix', 'lua'). `client_address` and
`client_port` vary based on the `client_type`.

Fixes #1201