Keep Visual Studio Code Insiders edition updated on Slackware.

Script manages installation of VSCode Insiders, which is installed
into /opt/vscode-insiders, and when this package is removed
(vscode-insiders-updater) it will also remove managed installation
from /opt/vscode-insiders.

By default script will be called from cron daily task, and it can be
run directly: /opt/vscode-insiders-updater/vscode-insiders-updater.sh
as root.

Script will then install or update VSCode Insiders edition, or do
nothing if you already have most recent release.

It can also be run more frequently since it makes just one HEAD
http request to check version.

Reinstall of VSCode Insiders can be forced regardless of installed
version with `--reinstall` flag, for example:

/opt/vscode-insiders-updater/vscode-insiders-updater.sh --reinstall