Remove ez_setup from setuptools installation docs
    
This removes ez_setup.py from the setuptools development instructions
and updates some links into EasyInstall that were skipping over the
deprecation warning.

Update recommendation.

Co-Authored-By: jaraco <jaraco@jaraco.com>

Document using setup.cfg for src-layouts

Document building Cython projects instead of Pyrex

Exclude .pyc in sdist output

Added minumum column in metadata table and version info for long_description_content_type

This also documents that the long_description_content_type keyword was
added in version 38.6.0.
Co-authored-by: Gene Matusovsky <gene_matusovsky@s5a.com>

This should stop the PyPI release stage if a `.pyc` exists in the
generated SOURCES.txt.

Mark Py 2/3-only tests as skip instead of xfail

* Update setup.cfg documentation to include data_files

Refs #1395

Fixes #1414

Officially support Python 3.7

Fixes https://github.com/pypa/setuptools/issues/1528.

Also reuse pre-defined py2_only and py3_only decorators where
appropriate.

Fix easy install warning #1525

Adds call to os.path.abspath() in pkg_resources.normalize_path() on Cygwin

Add data_files support in setup.cfg

This adds the `[options.data_files]` section to the existing setup.cfg
example.

In the test case, dist.data_files needs to be sorted because the
current implementation loads the configuration files as a dictionary
with arbitrary order on Python < 3.6.