Consolidates the multitude of CI systems, replacing Azure, SourceHut, and
AppVeyor with GitHub Actions, which now also runs clippy and fmt. See #352
* Add task to run clippy
* Add task to check formatting
* Test on 1.44.1 toolchain
* Update readme: status badge and downloads on GitHub Actions
* Remove strip binary task, leave it unstripped to allow debugging for now
* Rename task to install dependencies
* Remove Azure Pipelines
* Remove sr.ht SourceHut CI
* Remove AppVeyor
* Add first action
* Install libxcb-composite0-dev, fix job name
* Use apt-get instead of apt, more descriptive names for os-specific steps
* Also match .exe, thanks windows
* use upload-artifact v2
* Specifically pick out the binary for upload
* Fix step name
* Name binary after target os
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