Drop Python 3.5 support

[joshthoward]

This PR includes the following updates:

1. Dropping Python 3.5 support
2. Removing Python 2 type annotations

[hashhar]

For removing Python 3.5 you also need to update the setup.py python_requires AFAIK.

[joshthoward]

@hashhar disregard Mac OS and Windows support... I need to think about whether we want to run docker on each of those platforms or if we should have another service up and running for integration testing.

[hashhar]

I'm not so sure about the f-string changes (others may disagree) - they are readable in some cases but not in others. Also, can IDEs/static analysis tools catch cases where a f-string references a non-existent/mis-spelled variable?

e.g.

return "MAP({}, {})".format(
    self._format_prepared_param(keys),
    self._format_prepared_param(values)
)

vs

return f"MAP({self._format_prepared_param(keys)},
    {self._format_prepared_param(values)})"
```.

Also, are we using mypy in CI to actually verify the type annotations we have?
What end-user behaviour is for people who try to install the package for an unsupported version of Python?

[hashhar]

Looks good.

@joshthoward What does a user trying to install on Python3.5 see? Do get the older version? Or does it silently fail?

[joshthoward]

@hashhar It complains if you try to use Python 3.5. See below:

% pyenv virtualenv 3.5.10 test
Requirement already satisfied: setuptools in /Users/joshthoward/.pyenv/versions/3.5.10/envs/test/lib/python3.5/site-packages
Requirement already satisfied: pip in /Users/joshthoward/.pyenv/versions/3.5.10/envs/test/lib/python3.5/site-packages
% pyenv activate test
% pip install .
Processing /Users/joshthoward/Documents/GitHub/trino-python-client
trino requires Python '>=3.6' but the running Python is 3.5.10

[hashhar]

Awesome! It's a useful error message. I wondered if it was something cryptic and would make the 3.5 users confused about why installs broke.