Refactoring and bug fixing

[Kriechi]

Here a list of things this PR addresses:

• update and fix gem dependencies
• use fail instead of raise for asserting
• use tidy executable in current $PATH if available, else fallback to gem-included version
• only check HTML-ish files, prevents errors for PDFs and other stuff
• split HTML and CSS into separate runners - allows disabling of one part with HEADHUNTER_CSS=false
• use the correct url for each validation if available

Let me know which parts you like, maybe you want to cherry-pick only certain commits - which is fine with me.

[houndci-bot]

Line is too long. [88/80]

[houndci-bot]

%x-literals should be delimited by ( and )
Do not use %x unless the command string contains backquotes.

[jmuheim]

I think I used backticks for executing system commands. What's better?

[Kriechi]

Actually you used Open3.popen3 - but I couldn't find a specific reason - so I changed it to use standard ruby invocation.

[jmuheim]

Thank you, @aaronjensen! I will have to take an in-depth look at this. I'll try to do this soon.

Tell me, did you successfully use this gem? It was something like an experiment when I wrote it, and I didn't receive much feedback, so I didn't work on it anymore.

[aaronjensen]

Hi @jmuheim, I wasn't able to successfully use it, no. I had more luck with this pull request by @Kriechi, but it still caused several of my tests to fail. I'm really only interested in detecting unused css rules and I couldn't get deadweight working either so I tried this.

For now I used this: https://addons.mozilla.org/en-US/firefox/addon/dust-me-selectors/

but it would be great if there were an automated tool I could add on to my tests that'd give me a more accurate picture.

[jmuheim]

Which PR by @Kriechi do you mean?

It's good to hear I'm not the only one interested in detecting unused CSS. Maybe we can give this project some new fire together?

I don't have much time at the moment, but I certainly will in a few weeks. Which project do you want to use it for? Is it public, so I could try to get it to run?

[Kriechi]

This PR. I created it a couple of months ago - so I'm not fully aware of the changes I made any more...
My main point for this PR was to split HTML and CSS detection because the HTML-framework I used was spitting out a lot of errors.