I expect this to become the default way to test Windows builds and
create installers on Travis. The idea is that instead of downloading the
pre-built MXE binaries we might as well use a container that has all
this installed and can be used locally to test if things fail on Travis;
which will allow us to have the exact same environment for testing
locally as runs on Travis.
At this point the container used is way too big - more effort needs to
be spent on shrinking it.
Right now this only deals with Subsurface and not with smtk2ssrf.
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
