[css3-lists] Moved the predefined list styles

I've moved the predefined list styles to a separate document, as we
resolved in the telcon today.  I've placed it at
<http://dev.w3.org/csswg/css-counter-styles/>.  I've kept the 2.1
styles in the original Lists spec at
<http://dev.w3.org/csswg/css3-lists/#predefined-counters>, with an
issue about the CSS2 styles (there's actually a good half-dozen that
didn't make it into 2.1).

Is this satisfactory to everyone for now?

~TJ