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 removes the releases section to make the creation of new releases a
bit simpler.

This adds documentation stating that Alacritty supports the synchronized
update escape, which was implemented in 9575aed.

Since tmux does check terminfo for this feature, the `Sync` capability
has also been added. Tmux's implementation can be found here:

https://github.com/tmux/tmux/blob/f5b7ebc540fe3db5c3a5fe97d01de44551e76058/tty-features.c#L185

This fixes the shell completion by removing the flags removed from the
CLI in 0768428 and adding the new options flag.

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

Alacritty's description in the readme and manpage has always been a bit
overly aggressive in its marketing. This new updated text should more
accurately describe Alacritty's current state without pointlessly
agitating people.

Previously the _NET_WM_ICON would use the .ico which was also used for
the Windows icon. This icon used the dimensions 256x256, but the maximum
supported image size is 192x192, so a new image with the dimensions
64x64 has been added.

Since we know the image format anyways, the `image` dependency could
also be easily replaced with `png`, which cuts out a few extra unused
dependencies.