Instead of having the extra symlink in the root, this puts the symlink
in the alacritty crate. Since we build the package on Linux this is not
a problem and even allows us to get rid of the `alacritty.png` symlink.

To avoid having complicated symlinks with regards to the windows build
assets directory, it has just been removed from the `extra` directory
completely. Since we only need it for building, it doesn't matter where
it's located and users will never have to interact with it manually
anyway.

Closes #6242.

This commit swaps source and target for the windows asset symlinks,
since creation of a symlink is not possible on Windows systems without
administrator permissions.

By making the files inside the source folder the source instead of the
destination, a build is still possible without requiring elevated
privileges.

Fixes #5338.

This is only an update to the development version and does not represent
a stable release.

This is only an update to the development version and does not represent
a stable release.

This is only an update to the development version and does not represent
a stable release.

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.

This is a bump of the development version and does not represent a
stable release.

Fixes #2651.