Added an html validation check by looking at Nokogiri errors

[akoeplinger]

I know you said in #30 you're not interested in validating HTML, but Nokogiri already looks at the markup and provides errors when parsing, so providing basic validation is quite easy.

This simple checker helped me catch a few mistakes in my site, so I thought I'd try and see if you find it useful now 😄

[gjtorikian]

All right, I am less grumpy about this now. Plus I like that it's a separate, non-default option.

Can you update the README with the new option? Everything else looks grand.

[parkr]

Isn't this superfluous?

[gjtorikian]

In what sense?

[gjtorikian]

Ah, because get_checks would've deleted it above?

[parkr]

Yeah. If I want to run this check directly, I shouldn't need to know about the validate_html option, should I? If I'm calling it directly, the understanding would be that validate_html would be true. This is useful if I want to validate the HTML in some documents, but not all.

[gjtorikian]

Yeah, you are correct.

[akoeplinger]

I copied this from the favicon code:

html-proofer/lib/html/proofer/checks/favicon.rb

Line 12 in c30c183

return unless @options[:favicon]

Do you still want me to remove it here?

[parkr]

i think both should be removed

[akoeplinger]

Added docs to readme, let me know if there's something else I can do.

[gjtorikian]

@akoeplinger I would agree that the favicon unless should be removed, too. Once that's done I'll merge. Thanks!

[akoeplinger]

@gjtorikian sorry if that sounds pedantic, but I'd like to keep this PR focused on the new feature and not change unrelated code.
I can send a new PR that removes the favicon unless if you want.

[troyswanson]

😌 👍 🎉

Glad this is making its way in!