[Speed] pyperformance drops Python 2.7 support

Hi,

Python 3.9 introduced incompatible changes which broke Django and Tornado benchmarks of pyperformance. But Python 2.7 support prevented me to upgrade Django and Tornado which were stuck to Django 1.11.x and Tornado 5.x.

I decided to drop Python 2.7 support in pyperformance to support Python 3.9. So I was able to upgrade to Django 3.x and Tornado 6.x. PyPy is still supported but only PyPy3 (basic support, no benchmark is adjusted for PyPy JIT compiler).

So if you want to compare Python 2 to Python 3, you will be limited to pyperformance 0.9.1 which supports Python 2.7 and Python 3.8.

Victor

Night gathers, and now my watch begins. It shall not end until my death.