[FEATURE REQUEST] Adding inline annotations

[teolemon]

What

• Adding the possibility to add inline annotations (useful for Pull Requests)
• Adding a tutorial on how to do so in the README

[Cyb3r-Jak3]

Thanks for the suggestion. I think this would be a good idea. However, it doesn't seem like something that would be straight forward as there isn't really a good way to get error information out of the validation process as it is just printed to console. This is something that would be easier with svenkreiss/html5validator#61, so I will wait for that to be merged before attempting this.