I don't recall a build that would fail on MSVC15, but not on MSVC14.
Testing with both of them provides little benefit, while causing huge
delays in builds on AppVeyor.

In due time this can be re-enabled or AppVeyor setup can be moved fully
to MSVC15 when it becomes released.

Last known commit to pass is b1018aec.

Including the build artifact alleviates the need to also copy the
portable ZIP over to github issues, in case the build artifacts ever
get lost.

changelog.txt not updated yet