Add requires python to setup.py; alternatively repackage with pep517 standard build tools. #82
Description
there is no requires-python setting set within setup.py, however, the latest version of screenplain (0.11.1) requires python 3.6.
It is not usable before python 3.5 due to the typehinted variables within the Settings class of the PDF file.
However, surprisingly, I was able to install both screenplain and reportlab on python 3.6, though that doesn't change that it would be nice to see screenplain have a minimum supported python version.