Fixed possible UnicodeDecodeError in setup.py on Python 3.6. [3.x]

Put the long description in setup.cfg, without replacing characters. See this error on Plone Jenkins, https://jenkins.plone.org/job/plone-5.2-python-3.6/1058/console

Develop: '/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form'
Traceback (most recent call last):
  File "/tmp/tmps_fh_how", line 14, in <module>
    exec(compile(f.read(), '/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form/setup.py', 'exec'))
  File "/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form/setup.py", line 61, in <module>
    'util.txt',
  File "/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form/setup.py", line 46, in <listcomp>
    for name in ('README.txt',
  File "/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form/setup.py", line 22, in read
    text = f.read()
  File "/home/jenkins/shiningpanda/jobs/65a48de5/virtualenvs/d41d8cd9/lib/python3.6/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 752: ordinal not in range(128)
While:
  Installing.
  Processing develop directory '/home/jenkins/workspace/plone-5.2-python-3.6/src/z3c.form'.

I have seen it go wrong for more packages the last couple of months. Locally I see no problem with Python 3.6, so it could be a problem only on one Jenkins node. But if it happens there, it might happen for other users too.

See another package where I initially fixed it by hacking something in setup.py, and then replaced it with setup.cfg in this commit: https://github.com/plone/Products.CMFPlacefulWorkflow/commit/eda6670f50436d2dea426a389563df1223760978

Difference in output is very little, but seems an improvement:

$ diff orig new
9948c9948
<   >>> id = util.createId(u'&#196;ndern')
---
>   >>> id = util.createId(u'Ändern')
9967c9967
<   >>> id = util.createCSSId(u'&#1593;&#1614;&#1585;&#1614;')
---
>   >>> id = util.createCSSId(u'عَرَ')

Or with screen shots.

Old:

New:

The new text is the same as the text that is actually in the file that we include: https://github.com/zopefoundation/z3c.form/blob/3.7.0/src/z3c/form/util.txt#L29-L57

zopefoundation / z3c.form

Fixed possible UnicodeDecodeError in setup.py on Python 3.6. [3.x] #98