This release pipeline creates all the official release binaries,
and publishes them as artifacts. Currently it can only produce
nightlies and custom builds; stable/testing release binaries are
untested.
This commit also splits up the pipeline in small bits, to both
improve readability, and to share code with the CI pipeline where
possible.
It turns out that Azure Pipelines has a lot of issues downloading
an artifact from your own project if it is triggered from a fork.
From what I could deduce, this is because the API requires a valid
token, which is not set (correctly?) when triggered from a fork.
As it is nicer anyway to publish the Windows Dependencies on GitHub,
it is now published there (and updated at least every week), and
we use the files from GitHub as our dependency.
