Drop Python 2 support

[and-semakin]

Python 2 has reached its EOL about 1.5 years ago. Even AWS Lambda is going to deprecate their Python 2 runtime soon. Supporting this old version of Python prevents using modern language features, for example, PEP-484 inline type hints (not those comments).

You can go the same way as guys from Pallets Project did and use the python_requires package metadata. It will allow you to release the next version without Python 2 support (let's say 6.0.0), but Python 2 users will still be able to download and use the latest available version with Python 2 support (let's say 5.1.5).

Is there any plan of dropping Python 2? What do you think?

[and-semakin]

As we can see here there are approximately 15% of installations still happening from Python 2:

[and-semakin]

Also, Python 3.5 is deprecated as well.

[jd]

Fine with me if you go with python_requires so older version are available for Python 2.
I'm fine dropping Python 3.5 too.

[and-semakin]

Did some experiments and found that it's safe to drop Python 2 support right away, without needing an additional release with python_requires that includes 2.7. Check it out: #293