Drop Python 2.7 support

Continuing to maintain backward-compatible support for python2.7 greatly increases the maintenance burden on contributors, scares off new contributors, forces additional dependencies, and prevents (or slows) the adoption of new features.

https://python3statement.org/

I would also recommend dropping support for python 3.5, but IMO dropping 2.7 is a bigger deal.

[hugovk]

Here’s the pip installs for hazelcast-python-client from PyPI for July 2021:

category	percent	downloads
3.8	45.34%	4,370
3.6	25.48%	2,456
3.7	14.03%	1,352
null	7.74%	746
2.7	5.38%	519
3.9	2.02%	195
Total		9,638

Source: pip install -U pypistats && pypistats python_minor hazelcast-python-client --last-month

[mdumandag]

@burakcelebi Maybe we can document the table shared above somewhere in the Python Persona research.