Add error/warning indication in compact format.

[oryband]

Related to issue #88.

CLI's compact format csslint --format=compact filename.css doesn't indicate if a line is an error or a warning.

Purpose of compact format is to make it easier to parse by programs. This way we can integrate CSS Lint's into Vim's syntax checking capabilities (using Syntastic plugin, if you must know). It is very relevant to state this kind of info.

Here's the current output, which should be fixed:

$ csslint --format=compact base.css

base.css: line 2, col 1, Expected RBRACE at line 2, col 1.
base.css: line 97, col 1, Missing vendor-prefixed CSS gradients for Webkit (Safari, Chrome), Internet Explorer 10+, Opera 11.1+.
base.css: line 35, col 3, Negative text-indent doesn't work well with RTL. If you use text-indent for image replacement explicitly set text-direction for that item to ltr.
base.css: line 57, col 1, Don't use IDs in selectors.
base.css: line 61, col 1, Don't use IDs in selectors.

My suggestion is to add a Error: / Warning: string at the begginning of each line. E.g:

Error: base.css: line 2, col 1, Expected RBRACE at line 2, col 1.
Warning: base.css line 57, col 1, Don't use IDs in selectors.

You're welcome to suggest a better alternative, of course. :)

[eriwen]

Will add this weekend unless someone gets to it before I do.

[nzakas]

@eriwen - it looks like this change may have gotten lost in the shuffle. Would you mind taking a look?