Required minimum Python version is missing from `setup.py`

[eldipa]

The call to setup on setup.py should have a keyword argument that defines the minimum Python version required for pyte.

Something like:

setup(name="pyte",
      version="0.8.1",
      packages=["pyte"],
      python_requires='>=3.7',
      ...
)

Despite setup.py defines correctly the classifiers and says it is for Python 3.7 and upwards, if no python_requires is set, no requirement exists.

I was able to install pyte version 0.8.1 on a Python 3.6 environment which it is not okay.

It may not be a super critical today, but if 0.8.2 introduces Python 3.7 syntax, it will break downstream.