Raise error on invalid Markdown links

[axic]

EIP-1491 has [WIP] under multiple sections. This is rendered as [WIP] but I'm not sure it is valid or not. Ideally a Markdown parser should be run on the files too in case it reports any failures?

[lightclient]

What sort of markdown failures would we want to capture? It seems like [WIP] is valid? I would think that Jekyll would catch any markdown errors. But it would make sense for eipv to validate things like the "are the template sections present", etc.