Add option to only display errors

[ndelangen]

I have a lot of html files and when I lint everything the terminal is spammed with a lot of success messages.

When there's 1 error amongst hundreds of files, it's hard to find which file is the culprit.

Can you add a options so this is muted:

htmlcs/lib/cli/hint.js

Line 54 in 8e376b6

console.log('No hint result.');