Killing off some especially uptight rules

After some polite debate on IRC I've removed a few of the more persnickety rules that don't really matter much and a few others that just don't need to be spelled out. Unclenching.
I did, but was then told (in polite terms) that it was a stupid rule. 

I was trying for consistency by treating URLs as a string, and we quote strings in other languages... but really quotes just don't matter in CSS URLs and it's just one more rule to try to slavishly follow for no good reason, so I got rid of it. By having no specific rule, the new rule is effectively "do whatever you want with quotes in URLs in accordance with the CSS specs." So it just wasn't worth mentioning at all.