Meta Tag Validator

Similar to link preview validators from Facebook and Twitter, IndieWebify.Me should have a validator that shows what meta tags are commonly understood. It would serve as a reference implementation of meta tag parsing broadly across the web but also what IndieWeb sites would use in reply contexts. It probably be tied to metaformats as the reference implementation/parsing spec.

It should highlight what values were understood (e.g. title, date, etc.) as well as show an example h-cite for how that _might_ be rendered.

This validator could incorporate #104 and list which tags aren't needed.

This was discussed today at IndieWebCamp San Diego.

Start by reviewing the existing Facebook and Twitter link preview validators and the discussion referenced in #104. Define the validator’s supported meta-tag values, the tags that are unnecessary, and the example h-cite output; done means it reports understood values and shows a reference rendering for IndieWeb reply contexts.

Written by the indexing model from the issue text.