Refer to setuptools' declarative configuration page for moving the static metadata into setup.cfg.

A few other notes:

• Use pyproject.toml for PEP 517 implementation, but keep setuptools as build backend for now
• A universal wheel is now built for both Python 2 and 3 compatibility (using [bdist_wheel] universal=1; when py2 is eventually dropped, then remove that section)
• Version is dynamically read from shapefile.py
• Remove the various Python 3.x classifiers, and just use Python 3, as this is an unnecessary maintenance classifier as old packages should work fine with future Python versions (Python 2.7 is the sole exception); add a few other classifiers
• Setuptools' author field is really designed to only hold one; move @karimbahgat as maintainer (same as README.md)
• zip_safe was removed as it's not needed
• Now setup.py is a simple wrapper, which some folks expect to see; it may go away someday