Configure which rules are errors and which are warnings

[kschaefe]

Per https://github.com/CSSLint/csslint/wiki/Command-line-interface the command line supports the ability to specify --errors and --warnings. I would like to be able to specify which rules that I use go into the error and warning categories. I haven't been able to find anything in the docs or the source that leads me to believe that this is implemented in the grunt plugin.

For instance, we don't support older versions of IE, so I want to make any rules about old IE versions into errors instead of warnings (like they are currently configured).

I would think that the options for each rule could change from true and false to 'error', 'warning' and 'ignore'. This would be an API change, but I imagine that you could keep the original values to perform there current behavior.