This is the very very last command that executes in the Cygwin build, since the next line is disabled. Of course, changing a directory is irrelevant. But that directory doesn't exist after the Cygwin build. So it fails. So the build failed ON THE LAST LINE THAT DIDN'T MATTER ANYWAY.

super-test.sh tests building the samples with cmake. Without installing a cygwin-specific cmake, it ends up invoking the Windows-native cmake which doesn't work at all.

I don't know why we've been installing our own. According to this these are already installed: https://www.appveyor.com/docs/build-environment/#mingw-msys-cygwin

Also use super-test.sh to test Cygwin; get rid of appveyor-cygwin.sh which tests the wrong thing.

VS 2015 is just too buggy. Working around the bugs is wasting developer time.

This change does not actually remove any of the hacks yet, so that we can undo this decision if there are significant complaints after the next release.

This reverts commit b50f6598.

This will break out MinGW, VS2015, and VS2017 builds into separate jobs.
While they will still probably build in serial, we'll at least get better
granularity on test results.

While the VS2015 build no longer depends on the MinGW installation as an
external capnp, I think testing the CMake MinGW build on Windows probably
remains worthwhile.

This is redundant since branches are usually open in order to become PRs, which get their own merged-with-master builds.

This AppVeyor configuration will do the following:

1. Download MinGW 4.8.5, if it doesn't already have it.
2. Build and install the entire project with MinGW.
3. Build and install everything that MSVC can build, using the MinGW external
   capnp tools.
4. Build the contents of c++/samples.
5. Zip up the contents of each install directory, which will be available for
   download as artifacts.

AppVeyor will autoconfigure itself if it sees this file, so you should
just have to:

1. Log into ci.appveyor.com. You can use a GitHub account for this.
2. Select "New Project."
3. Select capnproto from the list of GitHub projects.

Push to any branch, and AppVeyor should automatically build the new
commit. If you want to build a branch that you've already uploaded, you
can change the default branch in 'Settings -> General', then start a
manual build.

I used Dr. MinGW's appveyor.yml as a template for the MinGW download and
extraction code:
https://github.com/jrfonseca/drmingw/blob/2340928f5cbc0ba718e8dd160e027af7722383c8/appveyor.yml