Build / publish wheels on Appveyor

[tseaver]

Checklist from https://github.com/zopefoundation/zope.proxy/issues/24:

• [x] a copy of appveyor.yml from zope.interface or similar
• [x] someone with an Appveyor account (e.g. @mgedmin ) to enable this project
• [x] encrypted PyPI upload credentials in the appveyor.yml (no change required from the copy in zope.interface if @mgedmin is the one who enables the Appveyor account)
• [x] grant zope.wheelbuilder PyPI rights
• [x] push the appveyor.yml commit to master
• [x] (optionally) a push of a temporary branch that builds and uploads Acquisition 4.4.2 wheels

[dataflake]

Fixed by commits 0b17c44052436633d170f45a9f930252832da60d and e6725597ffef6b8748499cedb09b289cb0c14fb4