Added tool to edit and check doas.conf

This release introduces a new utility called vidoas (vi doas). This tool is a shell script which creates a copy of the doas.conf file, allows the admin to edit the file, and then checks its syntax for errors. If a problem is found, vidoas reports which line the error was on and asks us to try editing the file again. Once the new doas.conf file contains the proper syntax, it is installed and overwrites the old doas.conf file.

This tool is designed to assist admins and avoid introducing errors to doas.conf which might accidentally revoke admin access to the machine.