some AppVeyor files

Many people enjoy the Windows testing the cfbot runs on the AppVeyor
service.

You can also run this yourself without the detour through the commit
fest app. Attached are three patches that add .appveyor.yml files, for
MSVC, MinGW, and Cygwin respectively. (An open problem is to combine
them all into one.) I have been using these regularly over the last few
months to test code on these Windows variants.

To use them, first you need to set up your AppVeyor account and link it
to a github (or gitlab or ...) repository. Then git am the patch on top
of some branch, push to github (or ...) and watch it build.

This is just for individual enjoyment; I don't mean to commit them at
this time.

(Some of this has been cribbed from the cfbot work and many other places
all over the web.)

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services