Include Font Validator run in AppVeyor script

[texhex]

Given that a lot of expected users for this project do not use Windows, it might be a good idea to include an automatic run of a Font-Validator and capture the output as well,

This might indicate some problems on Windows the author of the font might not be aware.

[chrissimpkins]

Is the plan to create an approach that will support this testing for any fonts that use this tool for installs on Windows since you are building it on FSCW rather than Hack-Windows-Installer?