Since not all suggested clippy lints by stable clippy are supported on
the MSRV of Alacritty, this commit moves the clippy checks to the MSRV.
Unfortunately this will mean that our lints might be significantly
behind, however it ensures our CI never blocks any code that should be
valid.
Developers themselves of course can still run the latest clippy to
follow the up to date recommendations.
This removes all CI builds from travis-ci, due to their recent changes
in policy and harsh limitations on builds. With build times over 2
hours, it was a significant hindrance to development.
Instead of Travis CI, the CI is now split on Sourcehut and GitHub. Since
Sourcehut only supports Linux/BSD, all builds on those operating systems
are executed there. The GitHub Actions CI is used to build for
Windows/macOS, which are not available on Sourcehut.
Since asset deployment for releases requires builds on all platforms,
this is also done on GitHub actions. Though the new `upload_asset.sh`
script makes sure that migration in the future is fairly simple and we
do not tie ourselves to the overly complicated GitHub Actions ecosystem.
