[Checkins] [zopefoundation/zope.sendmail] 803168: Add an appveyor.yml

[Marius Gedminas]

  Branch: refs/heads/appveyor
  Home:   https://github.com/zopefoundation/zope.sendmail
  Commit: 803168f54350df2659e345d7ffa0ac9e6a14097f
      https://github.com/zopefoundation/zope.sendmail/commit/803168f54350df2659e345d7ffa0ac9e6a14097f
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2020-08-20 (Thu, 20 Aug 2020)

  Changed paths:
    A appveyor.yml

  Log Message:
  -----------
  Add an appveyor.yml

This one is based on zope.index's appveyor.yml, without the binary wheel
building and twine uploading (since zope.sendmail is pure Python).