[css-shapes] basic shape syntax in prose

Hey all,

I've received very consistent feedback that the section on basic shape
syntax is too difficult to interpret. So I've substituted the previous
definitions for prose descriptions:

This:

rectangle([<length>|<percentage>][, [<length>|<percentage>]]{3,5})

Becomes this:

rectangle() takes either four or six arguments of <length> or <percentage>


The prose also refers now to the rules for functional notation from Values
and Units [1], which actually makes the definition more precise (what was
in the draft before did not account for optional whitespace within the
parentheses).

Thanks,

Alan

[1] http://www.w3.org/TR/css3-values/#functional-notation