Notify users about Python 3.5 deprecation.

[alejandrosame]

Where?

We should let user know that we are dropping support for Python3.5 after the next planned release. At least this warning should appear:

• in the PyDP pipy page (https://pypi.org/project/python-dp/)
• as an interactive warning in console when the user does import pydp when Python version is 3.5.

Who?

PyDP package users.

What?

PyDP users should be encouraged to upgrade their Python to 3.6+ before we stop publishing wheels for it after the next release is out for a smooth transition.

Additional Context

Many packages are dropping support for Python 3.5 on January 2021, including pipwhich makes this python version out of the common distribution pipelines.

We can use as inspiration how other packages communicate Python deprecation like https://pypi.org/project/poetry (both in the pipy page and in the console output).

[festusdrakon]

Hey, I'd like to be assigned this issue to work on

[chinmayshah99]

Sure